An emergency warning has been issued for a vast section of the Leeuwin-Naturaliste National Park in the Shire of Augusta-Margaret River.

The warning area has expanded significantly since the emergency alert was first issued on Wednesday afternoon, with hot and windy weather expected to test containment lines.

"You are in danger and need to act immediately to survive. There is a threat to lives and homes," the Department of Fire and Emergency Services said on Thursday.

"If the way is clear, leave now for a safer place."

The fire started near the intersection of Caves Road and Calgarup Road in Boranup, almost 300km south of Perth.

Authorities said the blaze had burnt through almost 1200 hectares and was escalating due to a heavy fuel load on the park floor.

Premier Mark McGowan urged residents to follow official updates on the blaze.

"It's potentially going to jump Caves Rd later on today and if it does that it'll be into a farmland area, so that's in the proximity of more residences as well," he told reporters.

"There's very high fuel loads so it's obviously burning quite ferociously."

A large aerial tanker has arrived from NSW and another is expected to arrive on Thursday.

The WA coast is set for high temperatures and windy conditions on Thursday, with a forecast peak of 36 degrees Celsius for the Perth metropolitan area.

"We do expect conditions to deteriorate and to test the containment lines and bits and pieces that they've been doing overnight," DFES spokesman Adam Jasper told Perth radio 6PR.

More than 100 firefighters are battling the blaze, supported by water-bombing aircraft. An evacuation centre has opened at Margaret River Recreation Centre.

An emergency warning is also in place for people travelling along Quininup Road in Yallingup.

The fire is travelling fast in a southerly direction and aerial support has been sent to assist ground crews.

Australian Associated Press