Traffic on Perth's Kwinana Freeway has started moving again after it was earlier reduced to a standstill when a fire burning in a heavily populated area in the city's south closed the major road in both directions in the lead-up to peak hour.

Key points: This is the second fire emergency in the past 24 hours in Perth's south

This is the second fire emergency in the past 24 hours in Perth's south The freeway has now reopened, but traffic delays are likely throughout the afternoon

The freeway has now reopened, but traffic delays are likely throughout the afternoon Kwinana Freeway is the major arterial road from the CBD to the southern suburbs

The freeway — the main arterial road leading south of the city — was reopened at 4:00pm after being shut between Armadale Road and Russell Road for more than an hour, but long traffic jams slowed commuter traffic in both directions as people tried head home after work.

It is the second major blaze to hit the city's southern suburbs in the past 24 hours.

Trains on the Mandurah Line have resumed between Cockburn and Rockingham, but Transperth reports they are not running to the regular timetable.

Cockburn Station, located next to the fire zone, were reportedly very busy, with extra train replacement buses being deployed.

Delays were also reported on the northern Joondalup Line.

The fire closed the Kwinana Freeway in both directions. ( Supplied: Nick Casserly )

An earlier emergency warning for areas of Atwell and Success has been downgraded to an all clear as the fire is contained and under control, and no longer threatening lives and homes.

But a new watch and act alert has been triggered in neighbouring Spearwood, in an area bounded by Spearwood Avenue to the north, Cockburn Road to the west, Ocean Road to the south and Rockingham road to the east, including Hamilton Road and Entrance Road.

A separate watch and act alert remains active for the fire that first flared yesterday afternoon, covering the suburbs of Hopeland, Oldbury, Mardella, Serpentine, Baldivis and Wellard.

'Absolutely terrifying' as flames creep close to homes

The area affected included Atwell Primary School, Atwell College and the Cockburn Gateway Shopping Centre.

The fire started near the intersection of St Claire Gardens and Paradise Grove in Atwell.

The Department of Fire and Emergency Services said although there is no immediate danger, residents need to be aware and keep up to date in case the situation changes.

Loading

Atwell resident Kelly Prytulak said the flames came close to her home.

"My daughter came running in, said there was smoke in the park out the back of our place," Ms Prytulak said.

"By the time we got to the front yard, it was up in flames above everything, just going mad …

"[It] jumped the roads, it was terrifying, absolutely terrifying."

Kelly and Taya Prytulak, and their dog Angel, were threatened by the fire in Atwell. ( ABC News: Rhiannon Shine )

The Kwinana Freeway was closed in both directions just before 3:00pm and while it has reopened, motorists have been asked to avoid the area if possible.

Helicopter footage showed traffic jams extending for several kilometres from Cockburn Train Station.

Traffic banked up as the Kwinana Freeway was shut down due to a bushfire. ( ABC News )

A lot of smoke remains in the area and drivers are being told to use their headlights and drive slowly.

If you cannot see clearly, pull over, keep your headlights and hazard lights on and wait until the smoke clears.