An emergency warning remains in place for a bushfire that is threatening lives and homes across a string of suburbs in Perth's south.

More than 150 firefighters are battling the blaze which was reported at midday on Thursday near Baldivis, about 40km south of Perth.

Afternoons presenter Simon Beaumont has spotted helicopters refuelling at Thomas Park in Medina.



There is a bushfire emergency for parts of Baldivis and western parts of Mardella. pic.twitter.com/SF2c4kYAGS — News Talk 6PR 882 (@6PR) January 9, 2020

It has since burnt through more than 1,000 hectares in strong winds.

The blaze is moving fast in a northeasterly direction and the emergency warning applies across an area spanning 20km north to Casuarina.

Affected residents should leave immediately if there is a clear path, the Department of Fire and Emergency Services says.

07:42 PM -Bushfire EMERGENCY WARNING for parts of BALDIVIS, MARDELLA, HOPELAND, WELLARD, CASUARINA and OLDBURY in the CITY OF ROCKINGHAM and SHIRE OF SERPENTINE-JARRAHDALE: https://t.co/ZSEIQCTb4B — DFES (@dfes_wa) January 9, 2020

"You are in danger and need to act immediately to survive. There is a threat to lives and homes," the warning read.

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

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A watch and act alert has been issued for surrounding suburbs east of Kwinana Freeway and authorities are warning residents as far north as Cockburn to remain vigilant.

An evacuation centre has opened at Mike Barnett Sports Complex in Rockingham.