OLYMPIA - A state of emergency was declared in 20 eastern Washington counties, including Grant and Adams counties, because of multiple wildfires threatening homes, businesses and natural resources as fire crews continue to face severe fire weather conditions.

The proclamation was signed late Tuesday night by Lt. Gov. Brad Owen, acting for Gov. Jay Inslee, who is away on state business in Washington, D.C.

Firefighters are battling several fires in eastern Washington, including six that started Tuesday. The fires are threatening more than 500 homes, resulting in numerous evacuations and could result in additional damage, according to Mark Sewart, of the state Emergency Management Division.

Extreme fire weather conditions and a lack of available firefighting resources in the Pacific Northwest could hamper future firefighting efforts in the state.

The proclamation of emergency includes Adams, Asotin, Benton, Chelan, Columbia, Douglas, Ferry, Franklin, Garfield, Grant, Kittitas, Klickitat, Lincoln, Okanogan, Pend Oreille, Spokane, Stevens, Walla Walla, Whitman and Yakima counties. A burn ban is also now in effect throughout Grant County.

The proclamation provides for the use of the Washington National Guard and the State Guard in the event its resources are needed to protect public health, safety, and welfare; and directs state agencies to do "everything reasonably possible" to assist affected local governments in wildfire incidents, according to Stewart.

The state's largest fire, the Mills Canyon fire in Chelan County, has burned more than 22,500 acres and is being fought by more than 1,000 firefighters and support personnel. The State Patrol has mobilized local fire resources in that fire and a fire near Twisp in Okanogan County that sparked Tuesday night.

The National Weather Service has issued red flag warnings and fire weather watches for high temperatures and winds for much of eastern Washington through Friday.