SPOKANE, Wash. (AP) — Residents of hundreds of homes have been urged to evacuate as a wind-driven central Washington wildfire raced through nearby timber, sending up a towering column of smoke.

Fire spokesman Rick Acosta says residents of 860 homes have been told they should leave. A Chelan County emergency management spokeswoman said earlier Wednesday that at least another 800 homes were less seriously threatened.

By late Wednesday, there was zero containment on the Chiwaukum Creek fire burning about 10 miles north of Leavenworth. The blaze has prompted the closure of a 35-mile stretch of U.S. Highway 2.

A spokesman earlier estimated the fire's size at nearly 2 square miles, but Acosta said it's so smoky and the fire has moved so quickly that officials just don't know how big it is.

More heat and winds gusting to 25 mph are expected Thursday.

Worsening wildfire activity has prompted the governor's offices in both Washington and Oregon to declare a state of emergency, a move that enables state officials to call up the National Guard. In Washington, that declaration covers 30 eastern Washington counties.