Bushfire contained in Perth's south

Firefighters have contained a fast moving and out of control bushfire that threatened lives and homes in Perth's south.

A watch and act alert was downgraded to advice level for people in the western part of Oldbury in the Shire of Serpentine Jarrahdale.

People in an area bounded by Orton Road, King Road, Coyle Road and Casuarina Road were advised to evacuate the area or prepare to actively defend, with their properties and lives under threat.

But the fire was contained by about 6pm on Sunday, the Department of Fire and Emergency Services said.

The cause of the fire, which was reported at about 3.30pm on Sunday, is unknown.