Firefighters have gained the upper hand in the battle against a fierce blaze threatening coastal communities but authorities warn challenging weather conditions will test their defences.

The bushfire in the Shire of Dandaragan, about 170km north of Perth, has cut evacuation routes and razed more than 70,000 hectares of scrub since it was started by a fatal car crash on Monday.

Residents in the fishing shack villages of Grey and Wedge and the town of Cervantes remain under an emergency alert, with authorities saying it’s too late to leave.

The fire had tripled in size since Wednesday and residents should continue to take shelter to survive, Emergency Services Minister Stephen Dawson said.

“We’re not out of the woods just yet,” he told reporters on Friday.

“We are experiencing difficult weather conditions today and also over the weekend.

“Thankfully there have been no reports of property loss or loss of life.”

Fire and Emergency Services Commissioner Darren Klemm said it had been an “incredibly challenging” week.

“The fire is about 3km from [Cervantes],” he said.

“Containment lines have held firm in Cervantes and Wedge, while sand dunes are protecting the Grey community.”

He said back burning overnight had burnt out large pockets of fuel and firefighters continued to strengthen containment lines.

“While crews are using every tool available to bring this fire under control the situation is still very challenging,” Klemm said.

He said thunderstorms could bring lightning and ignite more fires, with little rain forecast.

An emergency warning remains in place for parts of Wedge Island, Grey, Cervantes, Nambung and Cooljarloo.

About 37 residents in Wedge and Grey chose to stay in their communities as the blaze burned through roads in and out of the villages.

Many others, including some of the 500 residents of Cervantes, evacuated north before the fire cut evacuation routes on Thursday.

Dandaragn Shire president Tony O’Gorman said some residents from Grey were rescued by boat from a beach on Thursday.

“Our fisheries vessel [in Jurien Bay to the north] and our marine rescue people went down and took those people off the beach because it was just too risky to leave them there,” he told ABC News.

The bushfire is moving in a westerly direction and is not contained or controlled, according to the Department of Fire and Emergency Services.

More than 200 firefighters are battling the blaze.

Two large air tankers from eastern states joined the battle against the blaze on Thursday.

Parts of Indian Ocean Drive and multiple surrounding roads have been closed in the area.

An evacuation centre at Jurien Bay Sports and Recreation Centre has reopened, while Nambung National Park remains closed.

A community meeting will be held at the facility late on Friday.

Temperatures are set to reach the high 30s over coming days, with squally winds predicted.

Residents along the Ashburton Coast have been warned to brace for extreme fire conditions on Sunday.