An out-of-control bushfire is threatening lives and homes south of Perth.

An emergency warning was issued for an area west of Nanga Townsite, south of Dwellingup in the Shire of Murray and Shire of Waroona after “extreme unseasonal conditions” on Saturday.

“The fire is still spreading with strong winds in difficult to access steep and hilly terrain,” the Department of Fire and Emergency Services (DFES) said in an alert on Sunday morning.

“The fire ground is experiencing fresh and gusty winds this morning, decreasing into the evening.

“People in the area should remain vigilant in case the fire behaviour escalates again.”

Residents are being advised to leave for a safer place if the way is clear and if not, to be ready to shelter in their homes.

DFES said the fire, which started in state forest west of Nanga, had burned through 1650 hectares.

Authorities said the bushfire was unpredictable and moving fast in a westerly direction.

—AAP