Perth's Kings Park alight, suburbs in haze

Major roads remain closed near Perth's CBD as firefighters continue to battle a bushfire at nearby Kings Park.

The fire started on the west side of the popular park at about 1am on Tuesday, causing haze over roads and homes in nearby affluent western suburbs.

The fire, which is believed to have been deliberately lit, has burnt about 16 hectares and 40 firefighters are on the ground strengthening containment lines.

Motorists are being advised to avoid the area.

Two other major bushfires also remain a threat to lives and homes across WA.

A watch and act alert is in place for residents around Gidgegannup, near the Perth Hills, after a fire broke out overnight.

The number of firefighters on the ground has been increased from 60 to 105 and crews have contained the blaze to burning pockets of bush.

A watch and act is also in place in WA's South West where a fire threatened homes in the Augusta township area.

The bushfire began near the Westbay Retreat Caravan Park.

Augusta-Margaret River Shire chief bushfire control officer Dave Holland said firefighters had saved multiple homes.

"We've managed to keep it away from a number of houses," he told ABC radio.

"As far as I'm aware (those from the caravan park) are all safe."

Major roads have been reopened in some areas with speed limits reduced due to smoke and fire crews on the scene.

Department of Fire and Emergency Services Chief Superintendent Ricky Curtis said a strong easterly wind was making it tougher for fire crews to fight both bushfires but significant progress had been made.

Fire crews are now mopping up and are expected to remain on site overnight.

Mr Curtis said there had been damage to infrastructure from the bushfires but no occupied homes are believed to have been burnt.