Sixteen large wildfires burning across central and eastern areas of the US state of Washington have destroyed more than 200 homes as thousands of people remain on evacuation notices.
Wildfires across the drought-plagued western US states have led residents to flee their homes as authorities scramble for resources to beat back the flames.
The fires in Washington state destroyed an area covering almost 1,500 square kilometres as more than 12,000 homes and thousands of other structures remain threatened.
The massive cloud of smoke began to lift on Sunday, according to fire officials, but as air quality improves, the fire's behaviour could become more erratic and intense.
"It's like a flue opening in a fireplace," said Suzanne Flory, spokeswoman for the US Forest Service and the Rocky Mountain Incident Management Team, quoted by the AP news agency.
"Smoke serves as a cap on the fire."
Flory said they would not know until Sunday night or early Monday how much the fire had grown on Sunday, but as of late afternoon, fire activity had been relatively quiet, adding that visibility and air quality improved during the day.
Meanwhile, a new firefighting mobilisation centre is being set up at Fairchild Air Force Base near the city of Spokane to help fight wildfires in Washington state. The base will be the staging area for 20 large fire engines and 10 water takers and will be run by a team from San Diego, California.
The new firefighting resources come one day after the US administration approved Washington Governor Jay Inslee's request for a federal emergency declaration to help firefighting efforts in the eastern part of the state.
Separately, planes and helicopters were making major liquid drops on a wildfire that broke out on Sunday afternoon near a ski resort in California's San Bernardino Mountains, bringing the first gains against the blaze.
The US Forest Service said the fire near Snow Summit Ski Resort south of Big Bear Lake has forced evacuation orders for about 400 homes, many of them cabins and vacation houses.
Meanwhile, firefighters and residents are bracing for a return to more intense fire activity in western Montana where wildfires have scored large areas and threatened some small communities.