Mr Gale said the "risk" was still there for locals in and around the fire zone and it would be well into the evening until the department could downgrade the warning level.

An emergency warning remains for people bounded by Nicholson Road, Harrisdale Drive, Wright Road, Ranford Road, Tonkin Highway and Armadale Road in Forrestdale, Harrisdale and Piara Waters.

Residents in these areas are still in danger and need to act immediately to survive.

A watch and act has been issued for people bounded by Armadale Road, Tonkin Highway, Rowley Road, Nicholson Road, Gibbs Road, Liddelow Road, Fraser Road and Ranford Road in Banjup, Forrestdale, Harrisdale and Piara Waters.

An advice has been issued for people in parts of Southern River, Forrestdale and Banjup.

John Bosco College, Harrisdale Senior High School, Harrisdale Primary School and Forrestdale Primary School will be closed on Friday as a precaution.

Mr Gale said it was unclear at this stage how the fire started, but investigations would begin on Friday morning.

He also said it was "quite likely" an out-building had been damaged in the blaze, but hopefully not totally lost.

"The full assessment will start happening tomorrow," he said.

There are reports cars and at least one shed in the fire zone may have been destroyed.

As the situation stands, homes north of Armadale Road and south east of Anstey Road are under threat from the blaze, which started just after 12pm near the intersection of Forrest Road and Tonkin Highway.

The bushfire is considered out of control and unpredictable. About 150 Career Fire and Rescue Service, Volunteer Fire and Rescue Service, Bush Fire Service firefighters are attending. Aerial support has been sent.

Homes, a shopping centre and other businesses have all been evacuated.

Evacuation centre set up

The Department for Child Protection and Family Support has set up a temporary evacuation centre at Armadale Arena.

Speaking from the centre on Thursday night, City of Armadale Mayor Henry Zelones said there was no sense of panic among those at the facility. But Cr Zelones said he had heard unconfirmed reports of a shed lost.

"As far as we know they weren't houses, they were sheds or some other out-buildings," he said.

"There are still no confirmed losses of houses, but they are under threat."

Forrestdale Primary School will be closed on Friday as a precaution, after students were evacuated on Thursday.

The mother of a student who attends the school said she heard water bombers circling when she received a text message from the school telling her the children had been taken to the school's library.

"We are currently all waiting at Neerigen Brook Primary School," she said earlier on Thursday. "They have told us they have started evacuating and there are buses waiting outside to take the kids here. Some of the parents are pretty upset, but we know the emergency services are doing their best. I feel for the families whose homes are under threat and are also worrying about their kids.

"Some of the mums managed to get to the school before the roads closed and they said the kids are pretty scared. For some of the kindy kids, it was their first day at school."

The Education Department confirmed that under the instructions of the DFES incident controller, students and staff from Forrestdale Primary School had been evacuated to Neerigen Brook Primary School. The children arrived safely at the school on Thursday afternoon via bus.

People told to flee shopping centre

Jared Whitehouse, the owner of the Forrestdale Laundromat, said the shopping complex on Hensbrook Loop had been evacuated about 2.30pm. He said police had told business owners and customers to leave.

“I just locked up and left. It was very windy, there was a fire along Armadale Road and it’s now jumped the road across,” he said. “This is the first time we’re experiencing a serious fire. It’s burning away from where our laundromat is.”

Mr Whitehouse said he hadn’t seen any horse owners start to move their horses when he closed his shop, but knew there were a lot of horses in the zone.

Fire moves towards Harrisdale

Nine News Perth reporter Rebecca Johns, who is at the scene, said the fire was roaring towards homes.

"This fire just seems to be getting a little bit away from them (firefighters) at the moment," she told 6PR radio.

"I'm standing here watching these flames at the moment and they are big, they are at the tops of trees. I'm actually getting wet at the moment from the water bombers. It is quite close to us. The wind is quite strong. It is just heartbreaking to watch, everyone is trying to do what they can to keep this fire at bay."

Cutting fences to get horses out

Local Jessica Fynn-Meyer spent the afternoon moving horses.

"We picked up five in Forrestdale and took them to one property in Oakford and another property in Roleystone," she said. "They belong to three different owners who couldn’t get them out in time.

We had to cut fences to get these horses out.

"The neighbour on the one side is a farmer and he helped us with the fence.

"The horses get really excited and can cause trouble. But the ones today were really well-behaved.

"People offer paddocks or stables all the time when there are fires, so sometimes the owners don’t even know where their horses are until it all calms down again.

"I heard one big riding school wasn’t able to move their horses because it was so quick."

"The firies have a hell of a job on their hands."

Conditions and instructions are constantly changing; click here to keep up to date with the situation and to see what you should do if your home is in a warning area.