The blazes, in the West Australian regional town of Geraldton, continued to burn out of control on Monday, with a watch and act alert issued for three areas.
"Tragically, one home has been lost," WA Emergency Services Minister Paul Papalia told reporters.
"Fortunately, though, no loss of life and no injuries, so that is a good thing and the owner of that home has been located and they're safe."
Detectives are investigating whether arsonists lit some of the fires that also claimed sheds and cars, and threatened hundreds of other properties, including an aged care facility.
"That is appalling behaviour, totally unacceptable and (police) are going to be focused on identifying the culprits and bringing them to justice," Mr Papalia said.
He was also scathing of drone operators flying their aircraft near the blaze.
"There has been an incredibly concerning situation where a number of people have been operating private drones in the vicinity of the fire," he said.
"This is ridiculous behaviour, incredibly dangerous and can impede, if not endanger, the firefighting crew in those aircraft and potentially result in loss of life and infrastructure.
"It must stop."
An emergency warning has meanwhile been issued for rural West River, about 400km southeast of Perth in the Shire of Ravensthorpe.
People in the warning area are being urged to head towards Ravensthorpe if it is safe to leave.
The mercury climbed over 42C in Geraldton, where hot, dry and windy conditions challenged about 200 firefighters.
Commissioner Darren Klemm said conditions had been challenging for firefighters, and a wind change in the afternoon was expected to test them further.
"The most significant fire that they're dealing with at the moment started on Friday, but then there's been a whole series of other fires that have been occurring as well," he said.
DFES incident controller Brent Allen said crews went from house to house battling the blazes and saved about 600 properties.
"We had firefighters in backyards having to get over fences to get to structures," he said.
"There were fires in the gardens around a school."
Firefighters had contained the blaze on Sunday night, but swirling, gusty 80km/h winds helped it flare up early on Monday, burning through about 160 hectares of vegetation and property in total.
"The good news is conditions are easing," Mr Allen said.
"We've still got our backs against the wall for little while today until the humidity comes up.
"Once that happens, we'll be able to get really stuck into the mop up ... and making everything safe."
The bushfire is moving fast in a south-westerly direction.
Residents in the warning areas have been told there is a possible threat to lives and homes and they should remain alert as conditions are changing.
About 600 homes have no power and multiple schools and roads have been closed.
Two evacuation centres have been opened.
The Bureau of Meteorology has forecast 20 to 30 km/h winds on Tuesday, with the chance of a thunderstorm that will bring little or no rainfall.
11°C