The fire, near Moxham Park on Whitehaven Road in Northmead, travelled up an escarpment on Sunday afternoon and towards homes on the street, with firefighters scrambling to protect properties.

One house could be seen on fire in aerial footage.

The Rural Fire Service rushed multiple crews to the scene and helicopters scooped water out of the nearby Parramatta Lake to dump on the burning home.

The blaze was deemed under control about 3pm, with firefighters and aircraft getting the upper hand and the threat to properties easing.

Further west in the Blue Mountains, a Watch and Act alert for the Great Western Highway at Faulconbridge was downgraded just before 6pm.

"The immediate threat to homes has eased," the RFS tweeted.

"Crews will remain on scene for the next few hours."

They were among 62 bush and grass fires RFC crews were battling at 5pm as a cool change slowly heads up the NSW coast on Sunday afternoon.

Earlier, RFS Commissioner Rob Rogers said the service was deploying "overwhelming force" to attack every major blaze.

On Sunday, Sydney sweltered through the second day of a heatwave that saw overnight November minimum temperature records tumble.

Observatory Hill in central Sydney recorded an overnight minimum of 25.3C, shattering the November record of 24.8C set in 1967.

Damaging winds with gusts up to 90km/h are also hitting parts of Sydney as a low pressure trough passes over the area.

Australian Associated Press