Fire crews contain Perth fire

An emergency bushfire warning for Perth's southern suburbs has been downgraded, but fire authorities are urging residents to remain vigilant.

Firefighters have contained a fire that was threatening homes and lives in parts of Wattleup, Hammond Park and Success.

The Department of Fire and Emergency Services downgraded Saturday's warning to a watch and act alert, but advised that the fire was not yet fully controlled.

"The alert level for this fire has been downgraded as firefighters have been able to contain the fire, however people need to remain vigilant," the DFES said.

"If you are not prepared or you plan to leave, leave now if the way is clear."