Authorities say the Eyre Highway – Western Australia's main freight route with the eastern states – will remain closed until Saturday due to a bushfire burning in the Eastern Goldfields.

A 370-kilometre stretch of road between the Goldfields town of Norseman and Caiguna was closed on Wednesday afternoon after bushfires jumped the highway near Balladonia.

The Department of Fire and Emergency Services [DFES] and Main Roads WA have urged motorists to avoid the area, with people travelling west of Balladonia being redirected to Norseman. 

An estimated 160 trucks are parked up at Caiguna and there are 100 at Norseman.

The fire was first reported on February 7 but was upgraded to Watch and Act level on Wednesday as a heatwave spread across WA's Goldfields region, with temperatures hitting a high of 44.6 degrees Celsius at Norseman.  

More than 20,000 hectares of the Great Western Woodlands — the largest temperate woodland left on Earth — has been destroyed.

The cause of the fire is yet to be determined.

DFES incident controller Phillip Hay said conditions remained challenging and that the fire was burning close to the command post at Balladonia Roadhouse.

"We're working hard to build lines and contain the fire," he said.

"Unfortunately, we've had a number of breakouts."

Mr Hay said the highway would remain closed until at least Saturday and said people should delay any non-essential travel.

But he said trucks carrying crucial cargo would be escorted through the fire zone when conditions eased on Thursday night.

"We'll escort critical supplies through to make sure we don't have any issues," Mr Hay said.

"We know it's a major freight link … we'll have one escort leaving from Caiguna and one from Norseman."

Truck Driver Simon Morrison spent Thursday parked up in Norseman.

He was meant to make a delivery to Adelaide on Thursday afternoon.

Others made the most of the downtime — driver David Hawks spending most of the day "sleeping and watching YouTube."

Fellow driver Matthew was quick to secure a spot close to the bowsers, ensuring he had enough to run his freezers, stocked to the brim with frozen sausage rolls and meat pies.

Farmers take in livestock

It is the second time the Eyre Highway has been closed for an extended period this summer after bushfires near Fraser Range.

The closure of the only sealed road linking WA and South Australia has caused significant disruptions for freight providers and travellers.

Sam Starcevich, a farmer at Salmon Gums, said she had taken in livestock on transports heading across the border.

"We ended up with about 1,490 sheep here, two road trains, and a few other farmers around the Salmon Gums area took the others," she said. 

"You just do it don't you. You don't think about it.

It has been four years since raging bushfires closed the Eyre Highway for 12 days, trapping hundreds of motorists at remote roadhouses on the Nullarbor amid scorching temperatures during the holiday season. 

Covering more than 90,000 square kilometres between Norseman and the WA border, the Shire of Dundas is often forced to manage multiple remote fires.

Shire President Laurene Bonza said the fire had started more than a fortnight ago but the council didn't have the resources to fully extinguish it.

"We just get the regular word; 'monitor it' and then it runs into something quite large," she said.

"As in our 2019-20 fires that burned through 532,000 hectares; a significant patch of our Great Western Woodlands.

"It does immense damage to our diversity around here."