Watch and act fire alert in Perth metro

Lives and homes could be in danger from an out of control bushfire burning in Perth's south.

A watch and act alert has been issued for people in the southern parts of Wattleup and Hammond Park in the City of Cockburn.

The Department of Fire and Emergency Services said there was a possible threat to lives and homes as a fire was approaching the area and conditions were changing.

People need to leave or get ready to actively defend their property.

The cause of the fire, which started just after noon, is unknown.

People who live in the area but are not home are urged to stay away because conditions could be dangerous.