Residents are being urged to drink plenty of water and swim safely as sweltering temperatures intensify.
The mercury is tipped to reach near or above 40C in many parts of the state today, while Gosford is set to soar to 40°C, Mangrove Mountain 38°C.
Sydneysiders should experience a less extreme 38C, but temperatures in some western suburbs, such as Penrith and Liverpool, are expected to nudge over 40C.
A total fire ban has been declared for the Central Coast, Sydney and greater Hunter regions.
"The best way to reduce the risk of heat-related illness is to drink plenty of water and keep your body as cool as possible, and avoid prolonged sun exposure by staying indoors in cool or air-conditioned facilities," the Bureau of Meteorology said in a statement.
Surf lifesavers are urging those who head to the beach to watch themselves and loved ones for signs of heat stress, such as dizziness, fatigue and headaches.
They also want swimmers to stay between the flags.
We're also being urged to keep an eye out for the elderly and young children, encouraging them to drink plenty of water and limit time spent outdoors.
Also, don't forget to take extra care of pets and animals!