More than 200 firefighters have worked through the night to slow the head of the bushfire from reaching the north-eastern suburbs of the Western Australian capital Perth.

A "watch and act" notice, issued early on Monday morning, for Bullsbrook and surrounding areas replaced the emergency warning that had been current on Sunday.

While the blaze has not yet been fully contained, the fire is now stationary after a wind change from easterly to south-westerly on Sunday night.

"Firefighters are doing a burn-back in the UXO (unexploded ordinance) area where the unexploded area is and that will enable that area to be cleared," Department of Fire and Emergency Services spokesman Allen Gale was quoted by the ABC.

"That was the last area that we need to finish our containment line. Once that's complete, then we have the whole fire contained and under control," Gale said.

Many roads in the area remain closed as fire crews ensure the fire does not reach bushland that has remained unburnt for almost half a century.

"We don't want a fire to get into there because it's been 49 years since a fire's been in there (and) it's very high in fuel load," Gale said, adding that "If the fire got in there it would be very intense and very difficult for firefighters to control."

More than 6,650 hectares of charred landscape lies in the wake of the fire that started on Saturday.

Two derelict homes and five sheds have also been damaged.

The cause of the fire remains unknown, however police have said it was not deliberately lit.