Sutherland Shire Council was forced to stop visitors from entering Kurnell by 10.30am on Sunday after the peninsula reached "COVID-Safe capacity".
According to a post on the council's Facebook page, the suburb had reached capacity by 10.30am, and "control measures" were "actively employed on site".
"Those intending to visit Kurnell are advised to delay their visit until crowd numbers subside," A Facebook post said.
It is not known when, if at all, the suburb was reopened to visitors.
The Leader has asked the council for comment.
The council had put "active control measures in place to manage attendance on Kurnell" by 10am, as crowd numbers increased, and suggested those planning a visit to Kurnell "explore other areas of our Bate Bay coastline or delay your visit until crowds subside".
It comes after Sutherland Shire Council said on Friday it was bracing for big crowds at its beaches, parks, waterways and leisure centres over the weekend and into Australia Day, and warned beaches and car parks would close if they got too busy.
With many workers taking Monday off to give themselves an extra long weekend as Australia Day falls on a Tuesday this year, and a heatwave predicted, the council put extra traffic control measures in place, particularly around beaches and bays.
The council said that with more residents expected to spend Australia Day "enjoying our stunning open spaces this year", it was set to put a "range of temporary traffic management measures in place to ensure equitable access for those areas likely to be greatest in demand".
It comes after large crowds flocked to Cronulla in recent weeks, causing traffic chaos on all roads in and out of Cronulla.
Visitors have reported traffic queued back several kilometres on the Kingsway, while other routes into the area, including Burraneer Bay Road, have also been gridlocked.
Long-time residents said while increased traffic was common, especially on Sundays when the weather was good, there had been particularly long delays in recent weeks.
The council took to its Facebook page to urge beachgoers to avoid crowds, plan your visit out of peak hours, follow directions of lifeguards and police.
"Be aware that beaches and car parks will close when they reach capacity," the council said.
A council spokesman said visitors to the coast and bays should expect significant delays at many locations and needed to follow updates provided via message boards along the approaches to Cronulla and Kurnell.
Sutherland Shire mayor Steve Simpson said that with the forced scale-back of a number of large, popular community celebrations due to the ongoing COVID-19 pandemic this year, extra measures were being put in place to ensure local residents could still enjoy the both the lead up to Australia Day and the day itself in popular outdoor areas.
"We all know that Australia Day is an incredibly significant day for our country and community and that many local residents will be looking to gather with family and friends this year to spend the day enjoying our beautiful parks, waterways, beaches and other open spaces," he said.
"With demand expected to be greater than in previous years, Sutherland Shire Council will be using strategically placed signage and social media messaging to minimise the added strain on roads and parking facilities surrounding the areas we know will draw visitors."
The council said short-term parking for picks-ups and drop-offs would be provided throughout the weekend at Hordens Lane, Liverpool Street, Brighton Street and Beachcomber Avenue at Bundeena to manage an expected influx of visitors to the popular coastal community.
In addition to these measures, the council has been working with the operator at Boat Harbour four-wheel-drive park to reduce traffic queueing and to minimise the disruption to Kurnell residents as they traverse Captain Cook Drive, it said.
"We would urge all those who are looking to spend Australia Day enjoying our wonderful outdoor spaces to ensure that their celebrations remain COVID Safe, observe social distancing and follow all traffic control and parking measures put in place," councillor Simpson said.
"Please observe the signage in place and follow direction from council staff and those on site assisting with traffic control measures, ensure that you are parked legally and show patience with other motorists out on our roads.
"We also ask motorists to be considerate of the residents in the neighbourhoods where they are parking and recognise the residents still need to access their properties."
