The fire has blackened a four-mile-long stretch of hillside and cut power to Alcoa's Wenatchee Works smelter and hundreds of homes.
The Wenatchee World reports that no structures have been burned, but as many as 60 homes are threatened by the fire in the Malaga area.
Officials say about 40 homes remained under a Level 2 evacuation order Thursday morning.
The fire was first reported around 4:20 p.m. Wednesday along the Malaga-Alcoa Highway
The cause of the fire is under investigation.
There are no reports of injuries.