The massive blaze with a 126km perimeter has raced northwest across the city's coastal plain after destroying 71 homes near the hills town of Wooroloo on Monday night.
Gusty winds late on Wednesday pushed the fire towards homes in Avon Ridge Estate, Shady Hills View, Gidgegannup's north and along the Great Northern Highway.
But the blaze was stopped by more than 500 firefighters who battled tough conditions in steep terrain, and 11 air tanker sorties dropping 200,000 litres of fire retardant.
Western Australia's Department of Fire and Emergency Services, Superintendent Peter Sutton, says the fire came close to homes south of Bullbrook, where the RAAF Base Pearce is located.
"The fire ran up Avon Valley into Shady Hills and was successfully stopped by the retardant line," he told reporters on Thursday.
"But today we're going to experience strong easterly winds over the fire grounds which will test those western and northern boundaries.
"We expect there to be some concerns today, so we ask members of the public to be vigilant."
Properties near Walyunga National Park and the southern end of Great Northern Highway are likely to come under threat.
An alert has been issued for people in Shady Hills View, Bullsbrook's east and north of Gidgegannup.
"It's too late to leave and leaving now would be deadly. You need to shelter in your home in a room away from the fire front and make sure you can easily escape," the DFES said.
Federal Minister for Emergency Services David Littleproud said another large air tanker was on its way to Perth from NSW to help WA firefighters.
"We are very concerned about the fire and the events that will unfold today," he told reporters.
"Although the official count is still 71 homes that have been destroyed, we are bracing ourselves for further losses of homes overnight.
"Thankfully, there are no reports of anyone missing or loss of life."
The blaze has travelled 21km since it started near Werribee Road in Wooroloo on Monday. It's currently eight kilometres wide and more than 10,000 hectares in size.
"It's a very large complex incident in very difficult terrain and we have to get machinery in there which can be a long process, so this is going to go for at least a week or more," Mr Sutton said.
Weather conditions are not expected to improve until the weekend when rain has been forecast. In the meantime, the area is set to endure warm temperatures with strong winds and low humidity.
About 1200 homes and businesses in the region remain without electricity after the blaze damaged power lines and poles.
A DFES emergency warning remains in place for a large arc of land stretching west from Wooroloo to Upper Swan and north to Lower Chittering.
Evacuation centres have been set up at the Brown Park Recreation Complex in Swan View, Swan Active in Midland and Swan Active in Beechboro.
People whose homes have been severely damaged, or destroyed or who've been seriously injured in the fires will be able to access $1000 Commonwealth disaster recovery payments from Thursday.
Disaster Recovery Allowance payments will also be available for people who've lost income because of the blaze.