SEATTLE (Reuters) - Three firefighters in Washington state were killed and four injured while battling a wildfire threatening the north-central town of Twisp, Governor Jay Inslee said on Wednesday.

The deaths came as a fast-moving wildfire forced authorities late on Wednesday to order the evacuations of Twisp and Winthrop, towns in the foothills of the Cascade mountains, Okanogan County Emergency Management said on Facebook.

"I was just told that three firefighters died while battling the Twisp fire and four were injured," Mr Inslee said in a statement.

More than a dozen massive fires have blackened more than 400,000ha across the arid Western region, prompting fire managers to call in help from the US Army and abroad to reinforce civilian crews.

This week, the national year-to-date tally of area burned passed 2.9 million ha. That figure had not been reached so early in the year for two decades.