PERTH - Daylight in Western Australia has allowed helicopters back into the fight against bushfires still burning out of control in the Perth hills, where up to 40 properties have been destroyed.

On Monday morning, the bushfire emergency warning remained in place for people in the south-western part of Roleystone and south-eastern part of Kelmscott in the City of Armadale, as well as Baskerville, Millendon, Red Hill and Herne Hill in the City of Swan.

The Roleystone bushfire remains out of control and unpredictable, moving at 100 metres per hour in numerous directions.

The Fire and Emergency Services Authority (FESA) says 40 structures - including homes, sheds and carports - have been damaged or destroyed. The Buckingham Bridge on Brookton Highway has also been destroyed.

Authorities are warning lives and homes remain under threat with a fire approaching and conditions changing.

Two Type 1 helicopters and two Victorian Incident Management teams have joined more than 100 Victoria firefighters at the Roleystone fire, which started late Sunday morning and has burnt out 440 hectares.

Initial investigations by FESA and WA Police have determined the fire was accidentally sparked by a person using a grinder.

The Brigadoon fire started Saturday night, when a tree branch, which fell due to strong winds, came into contact with electrical transmission infrastructure.

Heavy earth moving machinery is being used to build a containment line along the northwest sector of the fire, near Weir Road. More than 100 firefighters are at the scene.

FESA regional coordinator John McMillan says the fire service is 100 per cent committed to fighting the fires even though crews are tired.

"At the moment we have assessment teams out in the field, assessing the structures that have been impacted," he told ABC radio on early Monday.

"The 40 (homes) ... is expected to be revised upwards in the light of day.

"We haven't had loss of life. We are grateful for that but certainly there's a lot of trauma that goes with it."

Mr McMillan said neither of two big fires outside Perth is under control, and unpredictable and strong winds are expected on Monday morning.

"Our struggle will remain until we get some respite in these unusual weather conditions," he said.

"It's just the strength of the easterly winds. They were at damaging strength two days ago and they have maintained the consistency."

One firefighter has been injured and taken to hospital after he was believed to have been hit by a fire truck near Roleystone.

At least 12 people have been hospitalised with smoke inhalation.

Hundreds of residents have evacuated from Roleystone and the nearby bush-fringed community of Kelmscott and to escape the other big blaze at the edge of the Swan Valley to the north where homes, vineyards and farms are also threatened.

Relocation centres have been set up near both fires and residents of a nursing home in Kelmscott have been evacuated to a shopping centre.

Many roads have been closed in threatened areas and residents who have left will not be allowed back until the all-clear is given.

- AAP