The heatwave has affected train services throughout Sydney.
It has resulted in speed restrictions being placed on Sydney's North, Central and South-West regions.
Train speeds have been reduced by 10 kilometres an hour, restricting the speed to 90kph.
"Extreme heat speed restrictions have historically had very little impact on the punctuality of train services," said a Sydney spokesperson.
For the latest info go to www.sydneytrains.info/
Earlier On Triple M
NSW 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 on Wednesday, with temperatures in the northwest town of Bourke forecast to hit 45C.
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 some areas, including the greater 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.