Authorities say firefighters prevented lives and more homes from being lost in the blaze, that has been fought using hand tools as embers rained down kilometres ahead of the firefront.
An emergency warning remained in place on Monday for communities in parts of Blythewood, Coolup, Meelon, Nanga Brook, Oakley, Teesdale and Waroona in the shires of Waroona and Murray.
Fire and Emergency Services Commissioner Darren Klemm confirmed the property losses, saying five short-stay accommodation units had also been razed.
"For those families that have lost homes, we understand this could be a difficult time for them," he told reporters.
"We'll be making sure we're reaching out and providing support to them."
Fire and Emergency Services Commissioner Darren Klemm says his crews face a tough task. (Aaron Bunch/AAP PHOTOS)
The fire, which has about a 50km perimeter, started on Saturday in state forest west of the Nanga township and has burned more than 3000 hectares.
Mr Klemm said the cause of the fire was accidental and is believed to have been started by campers using a car battery to charge electronic devices.
"They were trying to recharge some phones or the like off their car battery and something's gone awry with that," he said.
More than 160 firefighters and support personnel are battling the fire with support from water bombers.
"The fact that there has been no loss of life is testament to the hard work of our firefighters and the strategic use of aircraft," Mr Klemm said.
"At its peak on Saturday night embers were spotting three to four kilometres in front of the head fire."
The commissioner said the fire was fanned by strong easterly winds over the weekend and ripped through forest areas with high fuel loads that had not burned for 15 to 20 years.
"The fire is burning through steep and hilly terrain with thick forest and old-growth pine that is very dry and difficult to access," he said.
The blaze is moving slowly in a westerly direction and is not contained or controlled, with crews working to build containment lines.
The blaze is moving slowly in a westerly direction and is not contained. (HANDOUT/DEPARTMENT OF FIRE AND EMERGENCY SERVICES WA)
"They are 90 per cent of the way there in terms of getting this fire contained," Mr Klemm said.
"In some instances, they're using earthmoving equipment and because of the steepness of the terrain in other areas, they're having to do with hand tools, rakes and shovels."
Firefighters have also faced danger from falling trees.
Mr Klemm said a water tanker had been damaged and a search and rescue team conducting damage assessments were forced to leave the fireground on Sunday due to the risk.
He said the blaze could be downgraded later on Monday if it does not break the containment lines, but the mop-up was likely to take a further six to seven days.
The Department of Communities has set up an evacuation centre at Murray Aquatic and Recreation Centre in Pinjarra.
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