Sydney to swelter in two-day heatwave

Sydney is set to swelter as a two-day heatwave sends temperatures soaring into the high 30s.

The mercury is set to hit 35C in the city and 38C in the west on Tuesday and Wednesday, according to the weather bureau.

Bureau of Meteorology forecaster Sarah Chadwick says temperatures are expected to cool on Thursday.

"We are going to have generally hot and dry northwesterly winds associated with these warm temperatures," she told AAP on Monday.

The heat is also expected to see drier conditions with relative humidity to reach 20 per cent through the Sydney basin and 40 per cent in costal areas.

Ms Chadwick warned that the hot northwesterlies often contribute to a higher risk of fire.

The Red Cross says heatwaves can be dangerous and reminded people to keep an eye out for the vulnerable.

"Remember to check on your neighbours because older people, pregnant women, children, those with a disability and people taking medications are among those who are more at risk in a heatwave."