A wildfire burning in the remote Pasayten Wilderness (WA) near the Canadian border has firefighters worried that it could explode into a much bigger problem.

The Farewell Creek fire covered only 1,760 acres on Thursday, but firefighters said hot temperatures and dry conditions could cause it to flare like the Biscuit fire in Oregon last summer.

As a result, nearly 1,000 firefighters were concentrating on building lines to prevent a major spread of the blaze, which is in thick forest north of Winthrop in northcentral Washington.

Fire managers consider it one of the two most troublesome fires in the nation, along with the Aspen fire in Arizona, said fire information officer Mike Ferris.

Ferris is part of a national crew that took over fighting the Farewell Creek blaze this week.

"It has the potential to become really large and really difficult," he said. "We want to get as far ahead of this as we can before the fire really begins to get difficult."

Smokejumpers tried to parachute to the Farewell Creek fire soon after it was spotted on June 29, but high winds and steep terrain prevented an early assault, Ferris said.