NSW Health is urging residents to take care in coming days as much of the state is forecast to experience severe to extreme heatwave conditions.
It comes as the NSW Bureau of Meteorology warns much of NSW will be affected by a heatwave that will last until next Tuesday.
The bureau has issued a three-day heatwave forecast for Friday, Saturday and Sunday, with severe heatwave conditions predicted for Sydney, while extreme heatwave conditions are expected in other parts of NSW, including the South Coast.
Acting director of Environmental Health Dr Adi Vyas said people should take extra care to prevent heat-related illness.
"Hot weather puts a lot of strain on the body, including dehydration, and can make underlying health conditions worse," Dr Vyas said.
"It also causes heat stress and heat stroke. People over 75 years, people with chronic medical conditions and people who live alone are particularly vulnerable."
He said people should start planning now for the heatwave by checking fridges, freezers, fans and air-conditioners are working properly.
He said setting the air-conditioner to cool on a setting of 24 degrees will keep you cool while helping to reduce electricity demand.
Other tips include putting jugs of water in the fridge and cool packs in the freezer.
"Also ensure your blinds are closed before the sun hits your windows," he said.
"Protect yourself during the heatwave by postponing or rescheduling your outdoor activities. Reduce the impact of heat by avoiding being outside during the hottest part of the day; keeping well-hydrated with water and looking after vulnerable neighbours and relatives."
You should also keep an eye out for signs of heat-related illness, which includes dizziness, tiredness, irritability, thirst, fainting, muscle pains or cramps, rapid pulse, shallow breathing, vomiting and confusion.
People showing severe signs of heat-related illness should seek urgent medical attention and call triple-0 in an emergency.
NSW Health is also urging people to continue to be COVID-19 safe during the heatwave.
"If you're able to keep cool at home using fans, air-conditioning and closed blinds, please do so and stay at home. That way, we won't compromise physical distancing in public indoor venues, such as shopping centres, libraries and other public buildings where people may seek respite from the heat," Dr Vyas said.
"If you do leave your home to attend other indoor spaces, please physically distance and wear a mask in places where you cannot maintain 1.5 metres distance from others."