PERTH has sweltered through its hottest night on record, and total fire bans are in place across the state in response to a continuing heatwave.

Temperatures in Perth peaked at more than 43C on Saturday, and dipped to a still-steamy low of 29.7C just after 3am (WST) on Sunday.

That beat the previous record of 29.3C in 1962. The mercury rose again to 39.7C in the city just after 9am.

More than 30 career and volunteer Fire and Rescue Service and Bush Fire Service firefighters worked overnight to put out a scrub fire near a University of Western Australia research facility at Jolimont, in the city's west.

One staff member had to be evacuated but no buildings were damaged, although some fences were destroyed.

Department of Fire and Emergency Services said about 30 hectares were burnt, but the fire was contained and under control early on Sunday.

Residents in Jolimont and Shenton Park were told to stay alert and take care when driving through the area.

The cause of the fire is being investigated.

Elsewhere, more than 100 Bush Fire Service and Department of Parks and Wildlife firefighters from Boddington, southeast of Perth, were fighting a fire near Pinjarra-Williams Road, and two hectares were burnt near Caversham Wildlife Park, north of the city.

The Bureau of Meteorology has forecast an extreme fire danger on Sunday for Perth, Mandurah, the Perth Hills, and parts of the Great Southern and the Upper Great Southern.

A total fire ban is in place for parts of the Midwest Gascoyne and Great Southern.

Fines up to $25,000 or jail sentences of up to 12 months apply if a total fire ban is ignored.