Wildfires burning across several arid states in the U.S. Northwest on Wednesday have also blanketed much of the region with unhealthy, smoky air, prompting warnings from officials.
Parts of Washington state, Oregon, Idaho and Montana were under air quality alerts, according to the National Weather Service, as thousands of firefighters battled some 50 large wildfires scorching those drought-stricken states.
Blazes burning across the U.S. West have charred nearly 1.6 million acres (648,000 hectares), roughly the size of Delaware, with Washington state and Oregon alone accounting for more than 1 million acres (400,000 hectares) of the tally, according to the National Interagency Fire Center in Boise, Idaho.
In north-central Washington, a cluster of deadly fires dubbed the Okanogan Complex jumped some 20,000 acres in size from the day prior to more than 280,267 acres (113,420 hectares) on Wednesday, after a blanket of cooler air lifted, kicking up winds and heat.
The fire, now the state's largest on record, was 17 percent contained on Wednesday, up from Monday's 10 percent.
Emergency management officials have issued evacuation orders for more than 2,000 residents in the area, and thousands more have been advised they may soon need to flee as well, said U.S. Forest Service spokeswoman Suzanne Flory.
Last week, three firefighters were killed and four were injured in an initial assault on a branch of the Okanogan Complex. So far this year, U.S. wildland blazes have killed at least 13 firefighters, four more than were killed in the line of duty during all of 2014.
About 50 miles (80 kilometers) to the south, fires have scorched 88,104 acres (35,654 hectares), and some 1,000 residents in the area of Chelan, a resort town at the foot of Lake Chelan, remained under evacuation orders with the fire about 40 percent contained.
This summer's blazes have stretched resources thin, prompting a rare enlistment of firefighting reinforcements from the U.S. military and abroad.
Dozens of fire managers and firefighters from Australia and New Zealand were preparing for deployment against the Washington wildfires, the U.S. Forest Service said.
About 200 U.S. Army soldiers from Joint Base Lewis-McChord near Tacoma have already joined the front lines in Washington, as have crews from Canada, the fire center said.