The massive fire doubled in size on Monday night as it raced down onto the city's coastal plain from the hills town of Wooroloo, as firefighters desperately tried to save lives and homes.
Western Australia's Fire and Emergency Services Commissioner Darren Klemm said the number of houses destroyed had jumped to 71 overnight, but no deaths had been recorded.
He said the fire's northern flank would come under pressure on Wednesday, with particular concern for Shady Hills Estate about three kilometres southeast of RAAF Base Pearce in Perth's northeast.
"We're going to see gusts to 70 kilometres an hour in that northwest corner of the fire there," Mr Klemm told reporters on Wednesday.
"Really difficult terrain, really steep terrain, and the message to the people in Shady Hills Estate and the outskirts of Bullsbrook is they need to enact their bushfire plan and consider whether they need to evacuate now.
"We're into day three of this fire today and it's going to continue to be a challenging fire for us for at least the next three or four or five days."
Rosa Park resident Stewart Brisbane's rural home is about five kilometres north of the Bullsbrook area.
"You could see the flames shooting across the sky yesterday morning it was moving that quickly. It was an awesome sight to see," he told AAP.
"But everything is looking good at the moment.
"Hopefully, by the time the winds pick up the big plane from NSW will have everything under control," he added, referring to the water bomber rushed over from the eastern state to fight the blaze.
Mr Klemm said weather conditions on Perth's outskirts may not improve until the weekend, with the potential of rain on Sunday. In the meantime, the area would endure warm weather with strong winds and low humidity.
He said those obliged to quarantine due to WA's COVID-19 outbreak were permitted to leave their homes.
Crews had faced "a difficult and incredibly fast-moving" blaze that was spotting 3.5 kilometres ahead of the fire front at its peak on Monday night. The fire has already burned through more than 9000 hectares.
People in a 25km arc of land stretching west from Wooroloo to the rural suburbs of The Vines and Brigadoon in Perth's northeast have been told it is too late to leave.
"You need to shelter in your home in a room away from the fire front and make sure you can easily escape," the latest warning says.
Residents of suburbs and towns including Ellenbrook, Gidgegannup, Upper Swan, Herne Hill and Bullsbrook have been warned conditions remain volatile and they should be prepared to defend their homes or leave.
About 2000 homes and businesses were left without power on Tuesday afternoon, Western Power said.
The state's electricity provider was not able to safely access the fireground to repair the damaged infrastructure and restore power, but was working with the Department of Fire and Emergency Services to remove damaged power lines and poles.
Evacuation centres have been set up at the Brown Park Recreation Complex in Swan View, Swan Active in Midland and Swan Active in Beechboro.