UP TO a third of the small West Australian town of Yarloop has been destroyed in a fire that is covering more than 50,000ha south of Perth.

More than 200 firefighters were brought in on Thursday night and today to fight the Waroona fire that destroyed 95 homes, the local pub, post office and several other properties.

The state's Department of Fire and Emergency Services said fatigue among firefighters was becoming an issue, and they could yet need to call on other states to help supplement crews.

The fire was also threatening other towns in the region, including Harvey.

Just 30 homes were still standing in Yarloop yesterday afternoon.

The fire was sparked by a lightning strike early on Wednesday morning, and emergency services said the fire had already burnt about 21,000ha and crews were still unable to contain it.

The fire also caused power shutdowns to about 7000 residents in the region, including at Waroona, Preston Beach and Dwellingup.