More than 20 homes have been lost in the Perth Hills area in Western Australia as firefighters work to contain a massive bushfire.

The fire started this morning in Parkerville and moved rapidly to surrounding areas, including Stoneville and Mount Helena.

The Department of Fire and Emergency Services (DFES) says 27 homes have been lost but there have been no injuries to anyone in the community.

Russell Jones from DFES says the fire burned through more than 250 hectares and involved more than 100 firefighters.

Some firefighters have suffered heat exhaustion, he says, with hot temperatures making fire-fighting extremely difficult.

He says sightseers must stay away from the area.

"We've had several reports that there are many people moving through the area looking at the damage and it is making our firefighting efforts extremely difficult."

The fire is throwing embers and has flames of 20 metres high.

Homes have been evacuated and people have fled to two emergency centres.

Mr Jones says he hopes a drop in winds and a cool change overnight will help firefighters control the blaze.

The blaze comes on the back of a heatwave in Western Australia over the weekend, with temperatures on Saturday reaching 44 degrees Celsius in Perth.

That heat is now moving across the country, with temperatures in Melbourne and Adelaide expected to surpass 40C for days this week.

Residents grab essentials as fire approaches

Earlier, one local resident, Peter, told ABC local radio embers were falling onto his home near Mount Helena.

He planned to secure his horses and grab a few essentials before leaving his property.

"We are going to get the hell out of here. We are leaving everything," he said.

"We are just taking our animals, our main clothes; we've got our tax files in a box. That's it.

"We are leaving everything else, it can burn, it doesn't matter."

Another resident, Gavin, evacuated from his parents' home.

"I saw the orange helicopter, it was probably two properties down, so it is coming towards that area, Mount Helena, pretty quick," he said.

Water-bombing planes are at the scene along with 70 crews from 17 brigades.

DFES says the fire could burn for days, and extra resources are being organised.

Road closures are in place including Richardson Road.