A bushfire emergency warning has been issued for residents in Perth's south, where a blaze is threatening lives and homes.

The warning applies to an area bounded by Rowley Road, Kwinana Freeway, Mortimer Road, King Road, Thomas Road and Nicholson Road in parts of Oakford, Casuarina, The Spectacles, Mandogalup, Banjup, Hammond Park, Bertram, Forrestdale, Aubin Grove, Wandi, Wellard, Anketell and Oldbury.

The fire was reported at 11:13am and remains out of control and unpredictable, moving quickly in a westerly direction.

Firefighters are actively fighting the blaze, which started near the Modong Nature Reserve in Oakford, around 35 kilometres south of Perth.

People in the area are urged to act immediately to survive, with motorists asked to avoid the area as some roads may be closed.

More to come.