FIREFIGHTERS are being brought in from around Western Australia to help fight a fire raging through Perth's semi-rural northeast.

More than 150 firefighters tackled the blaze near Shady Hills and west of Walyunga National Park in Bullsbrook overnight, saving at least 30 homes using 70 appliances and earthmovers.

There are currently more than 200 firefighters on the scene and more are coming from Geraldton and the south coast, says Department of Fire and Emergency Services spokesman Allen Gale.

Mr Gale said water-bombers are on standby.

The fire had consumed about 1200 hectares and while it slowed overnight, strong gusts were expected today, Mr Gale said.

Firefighters were strengthening containment lines and focusing on hotspots, he said.

Some fencing has been destroyed and so far there have been no other reports of significant losses or damage from the fire.

Trucks are banking up on Great Northern Highway, where traffic is being diverted, because the fire is burning in bushland nearby.

Mr Gale said driving in the area was dangerous as smoke was thick.

It's understood some residents spent the night in their cars when they were unable to return to their homes.

About 10 evacuees stayed overnight at a relocation point at Bullsbrook's Pickett Park Hall.

The Walyunga National Park, Bullsbrook District High School and Bullsbrook Community Kindergarten have been closed.

While the official cause of the bushfire remains unknown, sparks from a Kalgoorlie-bound freight train were suspected to have sparked a string of fires that became one large blaze.

The fires were first reported just before noon yesterday.

An emergency alert remains in place for people near Shady Hills, including in Shady Hills View, Gibbard Place, Clarkson Rd, Taylor Rd, Foaling Ridge and Auger Place, and west of Walyunga National Park between Stock Road and Walyunga Road to Great Northern Highway.