Authorities in the US have ordered the evacuation of thousands of people as fire crews battle wildfires across the Pacific Northwest.

On Wednesday three firefighters were killed and four others were injured in Washington state.

Authorities ordered the immediate evacuation of the small community of Tonasket, in north-central Washington, impacting about 1,000 people.

Around 4,000 households in the riverfront towns of Twisp and Winthrop, in the foothills of the Cascade mountains about 120km southwest of Tonasket, were also forced to flee the encroaching blaze.

The Twisp blaze is just one of more than 70 large wildfires or clusters of fires in several drought-stricken western states, the bulk of them in Washington, Oregon, Idaho, California and Montana, the National Interagency Fire Center in Boise reported.

Dozens of homes have been reduced to ruins in Idaho and Oregon in recent days.

The fires have stretched civilian firefighting resources, prompting authorities to call the US Army and Canadian crews to help, as well as mobilise personnel from Australia and New Zealand for the first time since 2008.

Seventy-one fire managers and specialists from those two countries were due to arrive in Idaho on 23 August.

US wildfires have claimed the lives of at least 13 firefighters and support personnel so far this year, four more than died in the line of duty during all of 2014, the interagency fire centre said.

President Barack Obama has directed his administration to consult with local and state officials while the threat persists.

The Twisp blaze has proven the deadliest.

Three US Forest Service firefighters in an engine crew died on Wednesday while battling the flames, which overtook their position after they were involved in a vehicle accident, Okanogan County Sheriff Frank Rogers said.

Four other firefighters were injured, one of them in critical condition with burns over 60% of his body.

The Twisp-area fire, part of a larger cluster of fires dubbed the Okanogan Complex, has burnt 7,873 acres (3,194 hectares) of rural brush and dry timber about 185kmnortheast of Seattle since breaking out on Wednesday.

As of late yesterday afternoon, crews had yet to establish firm containment lines around the blaze, a spokesman said, adding that suppression efforts across the Northwest had been complicated by "sporadic and erratic winds."

The blaze near Twisp was burning in Okanogan County, the same area impacted by last July's Carlton Complex fire, the state's largest on record, which destroyed about 300 homes as it burned 250,000 acres (100,000 hectares).

About 80km south of Twisp, the so-called First Creek fire was posing a renewed threat to populated areas after engulfing more than 68,000 acres (27,000 hectares), with 39 homes and 28 outbuildings destroyed days ago near the resort town of Chelan.

The First Creek blaze jumped containment lines on Wednesday evening, triggering road closures and prompting authorities to extend evacuation orders to some 800 people.