As coastal NSW residents swelter through a rare spring heatwave health authorities are warning the heat could be deadly.
The Bureau of Meteorology issued a severe heatwave warning for NSW's south-coast and Illawarra districts on September 17.
In Sydney, the mercury rose to 32 and 33 degrees on the weekend before a forecast 31 degrees on Monday, 33 on Tuesday and 34 on Wednesday.
Temperatures are 10 to 15 degrees above average and persisting for longer than usual for this time of year, according to the Bureau.
Relief will arrive mid-week with a cool change returning conditions closer to average.
It's estimated more than 60,000 people died due to heat during the 2022 European summer, which was the hottest on record before it was exceeded in 2023.
With the Bureau remaining on alert for El Nino to develop this spring, Australians in the east are bracing for hotter and drier conditions.
Both the maximum and minimum temperatures must be unusually hot for a three-day period for a heatwave to be declared.
This is because it becomes harder for the body to recover overnight from the heat of the day when temperatures remain high, and can cause heat stress.
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Most at risk during heatwaves are older people, babies and children, pregnant and breastfeeding women, people with medical conditions or who are unwell.
NSW Health's executive director of health protection Dr Jeremy McAnulty said simple measures could reduce the risk of heat-related illness.
Avoiding the heat by staying indoors, minimising activity, closing blinds and curtains early in the day and not waiting to become thirsty before drinking water.
"It's important you do not allow yourself to become too hot or dehydrated," Dr McAnulty said.
"If you don't have air conditioning, using a fan, wetting your skin with a sponge, spray or water-soaked towel can help to keep you cool."
The signs of severe heat-related illness include dizziness, tiredness, irritability, excessive thirst, fainting, headache, changes in skin colour, rapid pulse, shallow breathing, nausea, vomiting and confusion.
To cool down take a cold shower or bath if possible, or fully wet the skin while lying in the shade, and seek urgent medical attention.