Residents of Harvey are being urged to evacuate immediately as a wind change forces flames south towards the small South West town.

A bushfire emergency warning was extended on Thursday to cover Harvey, 140 kilometres south of Perth, after it was earlier issued for the nearby towns of Waroona and Preston Beach, where many residents have been forced to flee from the fast-moving blaze.

People in Harvey and surrounding areas are being advised by the Department of Fire and Emergency Services (DFES) to leave in a westerly direction along Uduc and Forestry roads, then south along Forrest Highway.

For all the latest updates, head to our live blog coverage of the fire emergency at Waroona and Preston Beach

Meanwhile, more than 100 Waroona residents in an evacuation centre in Pinjarra have been told to find emergency accommodation in town, as it will be three to five days before they can return to their homes.

DFES Incident Controller Greg Mair said the South Western Highway could be closed for a few weeks because a wooden bridge at Samson Brook had sustained severe damage.

Mr Mair said the Forrest Highway, the other main route south, also remained closed.

Key points: Bushfire emergency for towns of Waroona, Preston Beach, Harvey, Wagerup, Yarloop and Cookernup

Bushfire emergency for towns of Waroona, Preston Beach, Harvey, Wagerup, Yarloop and Cookernup Up-to-date alerts on the DFES website and emergency information 133 337

Up-to-date alerts on the DFES website and emergency information 133 337 More than 100 people at evacuation centre in Pinjarra

More than 100 people at evacuation centre in Pinjarra The bushfire created its own weather system, BoM said

Preston Beach remains cut off, but residents are being evacuated by boat.

Mr Mair said people in Harvey are being urged to leave, but there would be no forced evacuations.

The warning also applies to the Alcoa mine site and nearby properties.

Mr Mair said the Alcoa refinery was under threat and being actively defended.

In a statement, Alcoa said the fire has moved to the west of its Wagerup refinery and all efforts are being made to protect infrastructure.

The company said its Willowdale mine remains completely evacuated and will remain closed until the fire threat passed.

"There have been no reports of injuries to employees or contractors. The welfare of our employees is paramount and everything is being done to ensure employees in the refinery are safe," the statement said.

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Meanwhile, a man in his 20's was taken to Peel Health Campus after suffering burns to his upper torso.

Nine patients have also been evacuated from Harvey Hospital as the town remains under threat.

The fire front is moving fast, in a westerly direction, and an emergency warning remains in place for the area bounded by Willowdale Road, Johnston Road, Forrest Highway, Dorsett Road, Williamson Road, Mayfield Road and Nanga Brook Road, including the Waroona town site, in the Shire of Waroona.

People west of the South Western Highway are being told to leave in a westerly direction if it is safe to do so.

Aerial water bombers, at least 20 firefighting trucks from the Department of Parks and Wildlife (DPAW) and 40 appliances from the Department of Fire and Emergency Services (DFES) are being used to fight the blaze.

Waroona is home to about 2,500 people.

DPAW spokesman Benson Todd said the fire was first reported at 7.25 on Wednesday, and it was started by a lightning strike at Lane Pool Reserve near Dwellingup, 50 kilometres north-east of Waroona.

He said strong winds of 40 to 60 kilometres an hour had fanned the fire and pushed it towards Waroona.

Mr Benson said the decision to evacuate the towns was taken when embers started dropping in the streets.

He said there had been some unconfirmed reports that the fire has destroyed some buildings, but authorities had not been able to verify them at this stage.

There is a watch and act warning in place for people in an area bounded by Johnston Road, Willowdale Road, Forrest Highway, Riverdale Road and Logue Brook Dam and Clark Road to Nanga Road.

People are being urged to leave if the way is clear.

Hot, blustery conditions spark fears for cut-off communities

Sorry, this video has expired Aerial footage shows the bushfire burning at Waroona

Weather conditions were extremely hot and humid in the region today, with a top of 39C recorded in Pinjarra, and winds of up to 40 kilometres an hour.

Western Power said electricity had been cut to 7,000 homes, amid unconfirmed reports hundreds of power poles had been destroyed.

Up to 20,000 people who were expected to descend on the region from Friday to Sunday for the Southbound music festival in Busselton have been advised to take an alternative route.

Perth resident Mary-Ann Newsham said she was concerned for her mother who she has not had contact with since Wednesday evening.

Ms Newsham drove south from Perth today, but was stopped in Pinjarra and could not continue further to where her mother lives in Waroona.

"We've put three welfare calls into the police and the police have informed us that they are too busy to go and check on her," she said.

"Our belief is there is no power or phones in Waroona and she's frail. She's in her 80s and we can't get anyone to go and see if she is ok.

"I just think that she'd be feeling abandoned, you know .... no one has been around to see if she is ok. She'd be frightened.

"I would just like somebody, somewhere to say 'look, I'll just pop in and see that she is ok' and ring me and say she's fine and as long as I know that, I'll be happy."

'You can see the despair on their faces'

Waroona resident Melissa Young arrived at the evacuation centre in Pinjarra this morning with a family member's dog named Maisy.

Waroona resident Melissa Young with a family member's dog Maisy at the Pinjarra evacuation centre. ( ABC News: Roxanne Taylor )

Ms Young told ABC News she did not hesitate to leave at 11:30pm on Wednesday when she saw the glow of the fire approaching the town.

"The glow is scary enough," she said.

"And the ash is coming into the backyards and into the fences and the smoke's getting really thick so it was just time to get out, it's not worth it, it's not worth your life."

Ms Young said many other residents did not leave town.

About 100 people were at the shelter.

Volunteer Colleen Warr said they looked exhausted.

"The later they are coming in the more worried they are," she said.

"There's people that came in maybe 15 minutes ago and you can see the despair on their faces in comparison to the people who got told to leave and left early on.

She said many of those arriving at the centre are reporting some residents are reluctant to leave their properties and have decided to stay and defend.