Bushfire threat eases in Perth's south

Improved weather conditions have helped ease the bushfire threat in Perth's south as firefighters managed to contain and control a blaze, which was accidentally sparked when a wheel came off a boat trailer.

At its peak, the blaze reached an emergency level but the warning has now been reduced to an advice level for Hopeland, Oldbury, Mardella, Serpentine, Baldivis and Wellard.

"Although there is no immediate danger, you need to be aware and keep up to date in case the situation changes," the Department of Fire and Emergency Services warns.

Firefighters are strengthening containment lines and undertaking safety checks of the roads.

Some roads remain closed and motorists are asked to avoid the area or slow down due to smoke.

Residents and business owners impacted by the fire can apply for a restricted access permit to enter designated areas.

The blaze, which started at midday on Thursday near the intersection of Karnup Road and Young Road in Baldivis, has burnt about 1330 hectares.

Boat owner James Hamling said he was returning from a holiday in Denmark when his trailer collapsed and skidded along the road.

"I apologise to anyone that was affected by the fire ... I still feel sick about it now," he told Nine News.

Meanwhile, the all clear has been given for a separate blaze in Atwell, which came close to homes and a shopping centre, and caused freeway traffic chaos on Friday.