West Australian Premier Mark McGowan has warned arsonists “they’ll have the book thrown at them” after dangerous bushfires south of Perth and the loss of more than 80 homes in a blaze northeast of the city.

An emergency warning was put in place late on Saturday as six separate fires posed a threat to lives and properties, with one blaze at Mt Duckworth coming within three kilometres of the local township.

Heavy rain from an intense low-pressure system allowed fire crews to get the upper hand on Sunday, with the threat level reduced to a bushfire advice.

Police also began an investigation into the fires amid concern they were deliberately lit.

It that was the case, Mr McGowan said, it was the work of an “appalling human being”.

“And they’ll have the book thrown at them when they’re caught,” he said.

If someone has deliberately done it, well then that is just a disgusting, deplorable and disgraceful act.

“No doubt the arson squad will hunt them down and they’ll go to jail.”

The situation came after a week-long blaze north of Perth destroyed at least 86 homes and burnt through about 11,000 hectares.

Rain also helped crews bring that fire under control with Emergency WA downgrading the warning to a bushfire advice.

About 300 properties were still without power on Sunday after the fire caused significant damage to electricity infrastructure.

Almost 150 firefighters remained on the scene, mopping up and strengthening containment lines.

The cause of the fire was unknown.

Deputy incident controller Greg Mair said the blaze was now officially considered contained and controlled.

He said a number of roads across the region had been reopened and some locals were being granted limited access to their properties.

Now batten down for floods

Firefighter’s delight in the rain’s arrival may be premature, with the Bureau of meteorology predicting wild weather and possible flooding.

Heavy rain and damaging winds are set to hit southwest Western Australia as an intense low-pressure system moves across the state.

Wind gusts of more than 100 km/h and isolated rainfall totals of up to 100mm are possible across Sunday and into Monday.

The ABC reports that residents and businesses in Carnarvon, in Western Australia’s north-west, are already cleaning up after a “once-in-a-decade flood”.

Heavy rain from a tropical low caused flooding across the north-west of Western Australia last week, setting rainfall records in Carnarvon and Minilya.

The Gascoyne River, which peaked at 7.1 metres at Nine Mile Bridge on Saturday morning, is currently sitting below six metres.

The Bureau of Meteorology said the Gascoyne River flooded every 10 years, on average, with the last significant flood in December 2010, when the river peaked at 7.7 metres.

Department of Fire and Emergency Services (DFES) Superintendent Craig Smith said there had been 50 requests for assistance in the Carnarvon area.

“It certainly wasn’t as bad as it could have been if the river had [have] gone further up than the 7.1 metres, but certainly there will be some people impacted,” he said.

-with AAP