Authorities are hopeful improved weather conditions will ease the threat from an uncontrolled bushfire threatening Western Australia’s renowned Margaret River region.

The fast-moving blaze had ripped through more than 5000 hectares of the Leeuwin-Naturaliste National Park on Thursday night.

Residents on the eastern side of Caves Road were urged to leave as more than 150 firefighters battled to strengthen containment lines in hot and windy weather.

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WA’s Department of Fire and Emergency Services said conditions had improved throughout the evening but there was still a significant risk to the community.

Commissioner Darren Klemm earlier described the situation as “extremely serious”.

“A number of properties are under threat on or about Caves Road,” he told reporters.

“The safest option for people in this area is always to leave early. Don’t wait until the last minute.

“Strong winds, cave systems and (lack of) access for machinery are making it incredibly difficult to control the bushfires and people need to listen to the warnings that are being placed.”

The warning area has expanded significantly since an emergency alert was first issued on Wednesday.

Authorities are particularly worried about farming properties on the eastern side of Caves Road as a trough passes through the area from the coast.

Evacuation centres have opened in Margaret River and Busselton.

Mr Klemm said the cause of the blaze was yet to be determined, playing down the presence of WA Police arson squad officers in the area.

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

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

“It’s potentially going to jump Caves Road 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 on Thursday.

“There’s very high fuel loads so it’s obviously burning quite ferociously.”

Authorities have downgraded the threat from a separate fire in nearby Yallingup to “watch and act”.

An emergency warning had been in place for people west of Caves Road between Spencer Road and Johnson Road.

The fire was moving slowly in a southeasterly direction on Thursday night but was not contained or controlled.

Mr Klemm said the Yallingup bushfire had originated at a house which was believed to have sustained some damage.

-AAP