Man burnt while battling WA bushfire

A man has been seriously burnt and a vineyard has been destroyed, while hundreds of people have taken refuge at two evacuation centres as a bushfire ravages an area south of Perth.

An emergency warning remains for Waroona, Harvey and surrounding areas, including Preston Beach, in Western Australia's Peel and South West regions.

A man in his early 20s was burnt on his back while battling the blaze near Waroona on Thursday afternoon, a St John Ambulance spokesman told AAP.

Nine patients from Harvey Hospital were evacuated to other hospitals, while 11 wheelchair patients were taken from the nursing home to other regional facilities.

Drakesbrook Fine Wines owner Bernie Worthington said his vineyard, olive grove and orchard were destroyed, but amazingly his 17 rescue chooks and goats survived.

"It looks like a mushroom ash cloud in the sky, like an atomic bomb has gone off," he told AAP.

Authorities say fences have been destroyed in the fire zone and some livestock may have been killed.

A bridge on the South West Highway has also been burnt, which means it could be some time before the road re-opens.

The Department of Fire and Emergency Services warns lives and homes are in danger from the fast-moving and out-of-control blaze, and burning embers are likely to be blown around homes.

Melissa Young lives on a 90-hectare property near Waroona and was forced to evacuate with her dog on Wednesday night, describing the blaze as ferocious and horrific.

"The speed was insane, it engulfed everything," she told AAP.

There were also reports of some people being evacuated from Preston Beach by boat.

More than 170 people have registered with the evacuation centre at Murray Leisure Centre in Pinjarra.

Almost 50 people have also sought shelter at Leschenault Leisure Centre in Australind.

Residents have been told they are not likely to be able to return home for at least three days.

People fleeing their homes have been urged to bring essential documents, medications and a relocation kit with them.

Federal MP Andrew Hastie and state MP Murray Cowper met with residents to offer their support.

The blaze started in Lane Poole Reserve and is burning on both sides of the South Western Highway, with several roads and recreation sites closed in the area.

Meanwhile, a watch and act alert remains for people in an area bounded by Johnston Rd, Willowdale Rd, Forrest Highway, Riverdale Rd and Logue Brook Dam, and Clarke Rd to Nanga Rd, in the Shire of Waroona.

Western Power says more than 7000 customers are without power.

The fire, sparked by lightning, was reported just before 7.30am on Wednesday and has burnt more than 21,000 hectares.

Waroona had a large bushfire sparked by lightning early last year too, with one home and several other structures destroyed.