Emergency bushfire alert east of Perth

An emergency warning remains in place for a bushfire burning out of control in Forrestdale, south east of Perth.

There is an immediate threat to lives and homes and residents must act immediately.

The alert has been issued for an area between Armadale Road, Tonkin Highway, Oxley Road, Commercial Road and Weld Street.

Residents are being urged to leave now for a safer place if the way is clear, or prepare to shelter in their homes in a room with two exits and water such as a kitchen or laundry.

A temporary evacuation centre has been set up at Armadale Arena on Townley Street.

Department of Fire and Emergency Services spokesman Will Blackshaw said hot and breezy conditions could present challenges for about 100 firefighters attending the blaze after the temperature reached 41C in Perth on Tuesday.

"It's not too bad where we are at the moment but clearly the conditions are the biggest thing up against our firefighters," he told ABC radio.

"What matters in the next hour is construction of control lines and containing this fire, and getting some aerial assets just to knock down the intensity of some of this fire."

A "watch and act" notice remains in place for a surrounding area extending south to Rowley Road and west to Nicholson Road.