WA firefighters battle out-of-control blazes caused by arsonists

Emergency crews are battling to protect homes from six out-of-control fires lit by arsonists at Baldivis, south of Perth.

People are being evacuated from the eastern part of Baldivis after the fires were lit at about 3pm (WST) this afternoon.

Residents in the area are being urged to flee if the way is clear otherwise to prepare and actively defend their homes.

The fire is out of control and unpredictable, with burning embers falling ahead of it.

A number of residents told 9NEWS they say teenagers running out of the bush a short time before the fires started.

Meanwhile the long-burning fire at Northcliffe has been downgraded to an advice level, but many residents are still without power and water.

Western Power says some properties in Northcliffe remain without power and the Water Corporation warns that drinking water supply and pressure in the area might be affected.

Residents returning to properties with water tanks have been told to check with the information point to determine whether the water is safe.

The Department of Fire and Emergency Services says the fire is contained but not fully controlled.

Favourable weather conditions have stopped the spread of the blaze - which has burnt through 95,000 hectares - but there are still hot spots around the fire, DFES says.

Windy Harbour Road has re-opened from Northcliffe to the settlement, but several other roads remain closed.

South Western Highway from Middleton Road to Mandalay Beach Road could be closed for several weeks, with assessment of the highway to begin on Wednesday.

DFES warns people not to risk their own lives by trying to get around road blocks.