Updated | SES units called to hundreds of jobs including flood rescues during extreme weather event in St George and Shire

Update Wednesday

Sutherland Shire SES says it is still "managing multiple RFAs (requests for assistance) from the weather event over the weekend".

"Wet ground and strong winds can make trees unstable, as is the case for this gum tree on Kingsway [at Miranda] we had to fell yesterday.

"Please report any dangerous trees and branches to us, on 132500, so that we can continue to keep the Shire safe.

NSW SES and Fire and Rescue NSW attended a potential structural collapse in Engadine town centre on Tuesday. Old Princes Highway was closed between Woolworths and the Post Office.

Update Tuesday

Tens of thousands of residents in various parts of Sydney spent another night without power after the weekend storm.

Ausgrid advised at 11pm on Monday power had been restored to 75,000 customers and crews would continue to work through the night to restore electricity to the remaining 63,000.

"This is one of the worst storms we've had in 20 year - Thank you for your patience in this trying time," Ausgrid said.

About 8pm on Monday, power was restored to most customers in Grays Point, Gymea, Gymea Bay and Kirrawee.

About 3pm on Monday, power was restored to Arncliffe and Bardwell Valley.

However, about the same time, power went out in parts of Mortdale, Oatley, Penshurst, South Hurstville and surrounding areas.

Update Monday PM

The full impact of the extreme weekend weather in St George and Sutherland Shire is being realised as photos and reports of damage and other effects flow in.

Many residents are still waiting for power to be reconnected, with Ausgrid bringing in crews from other parts of the state to help with a massive amount of work in areas of Sydney.

In the southern suburbs, dozens of trees have been brought down, including "a monster", which crushed a car in George Street Rockdale.

Another huge tree fell across Rainbow Place, Kareela, blocking in some residents.

"It was very lucky no one killed or injured," a resident said.

"This is the third large mature that has come down in Kareela within a radius of 200 metres in the last two months."

The resident blamed "narrow nature strips, shallow soil and their 50-year age".

A huge tree toppled over and took out power lines in Prices Circuit, Woronora about 3am on Monday and was still there in the evening.

Sutherland Shire SES received nearly 400 calls for assistance.

At 10.30am on Monday, 155 of the requests were still outstanding.

About 120 SES volunteers from the shire's four units, Menai, Heathcote, Sutherland and Cronulla, responded to calls in the most difficult weather conditions.

They were supported by equal number from the Rural Fire Service, along with Fire & Rescue NSW brigades from the shire.

Deputy commander of the Sutherland SES unit Sam Corby said volunteers had been engaged in bushfire, storm and flooding events non-stop since October last year.

The last of their unit members on bushfire deployment returned from Cooma on Saturday just in time for more extreme weather of a different type.

"It's obviously pretty fatiguing," Mr Corby said. "Many have missed out on Christmas and other public holidays and family events.

"We are very grateful for the support from our families, employers and work colleagues."

SES volunteers evacuated about 20 people and their pets from Sandy Point about 11pm on Sunday night when the Georges River burst its banks and inundated homes in the lower end of St George Crescent and Gambier Street.

The water inside properties was about a metre deep.

About 8.30pm on Sunday, motorists had to be rescued from their cars on Taren Point Road and Parraweena Road, Taren Point. The area has a history of flooding.

Earlier in the day, cars were caught in floodwater from cars near the intersection of Alfords Point Road and New Illawarra Road, Menai, north of the Bangor Bypass.

"We have level three flood technicians who train at the Penrith Whitewater Stadium, and they go for a swim or a wade to get the people out of their cars," Mr Corby said.

Update

Woronora Dam has had a 25.2 per cent increase in storage in the last week as a result of the rain that has bucketed down over the last few days.

At 9am on Monday, Woronora Dam was at 59.6 per cent of capacity.

Overall Sydney dam storage has jumped by 21.7 per cent in a week to 63.6 per cent.

Update Monday

SES units in St George and Sutherland Shire received hundreds of calls for assistance and thousands of homes and businesses were blacked out in the horrendous weekend weather event.

On Monday morning, many households remained without power.

Train services have been severely disrupted on the T8 Airport Line, but the T4 Illawarra Line was expected to operate to timetable.

An amazing video by Greg Tannos, of Find My Australia, shows National Falls in Royal National Park "going off".

The water level at Woronora Dam has risen more than seven metres.

Sutherland Shire SES received over 230 requests for assistance, including six flood rescue jobs.

"It's been an incredibly crazy day out there and we appreciate the patience and responsibility our shire residents have displayed today, but we do urge everyone to stay out of floodwater," the service said on Sunday night.

"We are working our way through jobs as quickly as possible and will have teams out in the field into the night and over the coming days.

"We do still have many roads flooded so we ask that before heading out for work in the morning (or this evening for the night owls).

One job to which Kogarah SES responded was a tree that had fallen onto power lines and was suspended dangerously over Carwar Avenue at Carss Park.

The SES managed the road block and kept pedestrians (and their dogs) a safe distance while the energy contractors used an elevated platform and mobile crane to safely remove the tree from the power lines.

Once on the ground the SES broke the tree down into manageable pieces for removal then opened the road.

Hurstville SES received over 130 requests for assistance since Friday morning, leading to multiple teams being active throughout the weekend.

Jobs ranged from leaky roofs to flooded basements to downed trees.

Arncliffe, Bardwell Park, Allawah and Carlton were among suburbs still without power on Monday morning.

Power was restored about 5.30am to Kangaroo Point, Sylvania and Miranda.

Heavy and continuous rain caused widespread flooding of roads and properties.

The upside was the much needed boost to dams.

Live Traffic Sydney's reported road closures and other hazards on Sunday afternoon and evening included Audley Weir, Heathcote Road and Alfords Point Road, along with:

Rainfall figures for the weekend include: Peakhurst 325mm, Lucas Heights 278mm, Royal National Park 229m, Woronora Dam 244mm, Sans Souci 139mm, Cronulla South 146mm.

The Lucas Heights official weather station has recorded its wettest February day on record.

Sutherland Shire Rural Fire Service Inspector Scott Deller said rainfall at Lucas Heights was a record.

The previous record of 170mm was recorded on the February 3, 1990, he said.

"It is also the second wettest day on record for this location since 1958, with 232mm recorded on 11 July 1991.

"Sutherland Shire has seen well over 100mm of rain, with winds averaging 60km/h inland, with gusts near the coast reaching 100km/h.

"Given the significance of the event, our NSW Rural Fire Service crews have been assisting the State Emergency Service with storm-related damage, both within and outside the Shire, in addition to assisting Fire and Rescue NSW with fire-related calls, both within the area and further afield.

"We appear to be through the worst of it, with conditions slowly moderating over the coming days.

"Given the amount of rain that has fallen, riverine flooding, particularly in those areas impacted by tides, will continue to be problematic, both tonight and during tomorrow's very high tide.

"The SES has issued a number of flood evacuation orders, so please keep up to date and follow their page/s.

"The Woronora Dam catchment has seen good rainfall as well, resulting in the dam water level rising a staggering 7 metres."

Update Sunday

Thousands of homes and businesses have suffered power blackouts during Sunday's wild weather.

Impacted suburbs have included Miranda, Sylvania,Beverly Hills Lugarno, Mortdale, Oatley, Bardwell Park, Bexley, Bexley North

Sutherland Shire SES advised, "We have been absolutely hammered by this crazy weather today resulting in trees giving up and taking a dive, many taking out powerlines on their way down.

"If you see fallen powerlines always assume they are live and stay at least 8 metres away.

"Some roads have also been blocked by fallen trees, other roads have been affected by flooding.

"Stay safe Sutherland Shire - never drive, ride, walk or play in floodwater! And if you do need to be out on the roads today, slow down and drive to conditions."

Kogarah SES said, "It has been a very busy weekend so far for Kogarah Unit with 2 teams on flood rescue and 2 teams looking after local storm jobs. Teams will be working through jobs but please be patient as it is taking a little more time in this weather.

"There is still a severe weather warning current in the metro area for heavy rainfall, damaging winds, abnormally high tides and damaging surf."

Bureau of Meteorology acting NSW state manager Jane Golding told The Sydney Morning Herald the last time Sydney recorded as much rain was in 2016, but by the time the system passed it would likely rival a weather event in 1998 for the total rainfall recorded.

Some areas were already experiencing gale force winds, which indicated that the system was intensifying. About 15 to 20 millimetres of rain was falling per hour.

"We are expecting to see moderate flooding for some of our rivers and potentially it is not out of the question that we get major," Ms Golding said.

Earlier: Sunday

Roads have been flooded and trees brought down in St George and Sutherland Shire by torrential rain and lashing winds.

Cronulla beaches are also taking a pounding from big seas, with four metre high waves rolling in, causing the Esplanade to be closed.

"We have received reports of flooding northbound on New Illawarra Road with a number of cars stuck," SES Sutherland Shire advised about 11am.

"Police are in attendance and SES crews are on their way to the scene.

"We urge the community, please DO NOT drive through flood water!"

The road had since been cleared and had reopened.

SES Sutherland Shire also advised, "We are hearing reports of residents struggling to contact us via phone - understandably the 132 500 number is still experiencing a high volume of calls so we ask that should you need assistance, please be patient and keep trying. In the event of a life threatening situation call 000."

Live Traffic Sydney advised New Illawarra Road was closed northbound near Bangor Bypass due to a fallen tree.

Trees also came down on Taren Point Road, Taren Point, and Elouera Road and Elouera Road, Cronulla

Bexley Road at Bexley North was closed between Kingsgrove Avenue and the M5 East due to flooding.

The road was also closed for a period on Saturday.

Cronulla beaches are taking a battering, but so far it does not look like there will be a repeat of the devastation in June 2016 when huge waves sucked thousands of tonnes of sand into the ocean.

However, waves were breaking over the Esplanade between Cronulla and North Cronulla, causing the council to close the walkway.

Zimzala restaurant, on the Esplanade at Cronulla beach, prepared for the worst, moving equipment to higher levels.

But high tide at 9.08am passed with no repeat of the situation in 2016 when waves broke over the Esplanade and washed heavy, unsecured wooden benches into the walls of the restaurant.

Zimzala owner Ray Nelson said they made a decision at 9am to close for the day.

"The swell is still threatening and we could get some freak waves, but the situation is not like 2016, thankfully," he said.

"At high tide, we saw a couple of backwashes that went into the outdoor area of the restaurant, but that's nothing really."

Conditions could become more challenging later on Sunday another high tide, along with wave height and swell direction forecast to peak at 6pm.

Earlier - Saturday

Saturday's Sydney Derby has been postponed due to an unplayable pitch following the extreme weather experienced in Sydney over the last 36 hours, and further torrential rain forecast right throughout Saturday.

Sydney FC Chief Executive Officer Danny Townsend said: "Obviously we are disappointed to have to postpone the game, but the safety of the players is paramount and the pitch was in no state to host the game due to the amount of rain we have had.

"We also have to consider the safety of our Members and supporters inside the ground as well, and what sort of a spectacle we'd be providing if we went ahead.

Earlier - Friday

The Bureau of Meteorology issued a Hazardous Surf Warning, Marine Wind Warning and a Severe Weather Alert on Friday which will affect the Byron Coast in northern NSW through to the Eden Coast in the state's south. The SES has issued a Flood Warning for Mid North Coast and North Coast of NSW. The hazardous weather conditions are forecast to impact NSW from today, 7 February, through Monday 10 February.

Conditions are expected to be hazardous for coastal activities such as rock fishing, boating, surfing and swimming. People should consider staying out of the water and avoid walking near surf-exposed areas. Rock fishers should avoid coastal rock platforms exposed to the ocean and seek a safe location that is sheltered from the surf.

In addition to strong wind and high sea swell, the Bureau of Meteorology has also forecast significant rainfall which will impact water quality at many NSW beaches into next week.

Adam Hummerston the President of Cronulla Triathlon Club said their annual fundraising event for The Heart Foundation, "The Richie Walker Aquathlon" that was to be held tomorrow, has been postponed until the 21st March.

"Unfortunately water quality in Gunnamatta Bay has reached unsafe levels due to the rain last week and with the forecast looks set to get worse over the coming days, so in the interest of our competitors health we had to make the disappointing decision to postpone this event until the 21st March." Adam said

Joel Wiseman, Director of Lifesaving at Surf Life Saving NSW said that conditions across the weekend will be very dangerous.

"We urge members of the public not to engage in risky coastal activities. If people put themselves in danger in these extreme conditions, there's a real chance that lifesavers will not be able to save them," said Joel Wiseman.

With strong 20-30 knot winds and sea swells up to 5 metres forecast in some locations, there is a threat of coastal inundation, erosion and flooding in low-lying areas. Exacerbating the impact of strong winds and large swells is a very low-pressure system and high tides which will affect sea levels along the NSW coastline. Large tidal surges are a possibility in some areas.

In anticipation of the forecast hazardous surf and weather conditions, Surf Life Saving NSW has put additional Duty Officers and surf rescue assets on standby across the weekend. The Surf Rescue 30 Offshore Rescue Boat based in Sydney, Surf Rescue 40 and Surf Rescue 50 jetboats and crews will also be on standby in Ballina and Kiama to respond to any critical coastal incidents.