05/02/2017 7:19 AM AEDT | Updated 06/02/2017 2:27 PM AEDT

Sydney Set To Swelter Through Another Summer Scorcher

Very high fire danger is predicted across NSW on Sunday.

Getty Images/iStockphoto
Sydneysiders are bracing for extreme heat on Sunday.

Heat records are set to tumble again on Sunday with Sydney set for another summer sizzler.

The mercury was already at 29 degrees Celsius early Sunday morning, but is forecast to move much higher through the day.

In the west at Penrith it's headed for a top of 42 degrees while the city is predicted to reach 38 degrees.

If the forecasts are accurate, it will be the tenth time that the mercury has climbed above 35 degrees, which will be a new record, according to the Nine Network.

Weatherzone forecaster Joel Pippard told Fairfax Media that there was a "very high chance" the temperatures this month would match January's extreme heat.

The extreme heat has prompted the NSW Rural Fire Service to warn of a severe fire threat across much of the state on Sunday.

The Bureau of Meteorology (BoM) says relief from the heat will likely arrive in the evening, with thunderstorms forecast to sweep across the city.

Sydney is set to be by far the hottest capital city on Sydney, but Brisbane, Perth, Adealaide and Canberra are also predicted to experience 30 degree-plus days.

Melbourne, Hobart and Darwin can look forward to a cooler day, with max temperatures in the 20s.