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(CNN) -- Nearly a million acres were burning as 21 wildfires raged in the Pacific Northwest on Sunday, fire officials said.
The unconfined fires in Oregon and Washington, mostly ignited by lightning from thunderstorms that swept through the region a week ago, covered 942,247 by Sunday, Northwest Interagency Coordination Center spokeswoman Carol Connolly said.
The 21 large fires are the most the region has seen on the landscape at one time, she said.
According to Okanogan County, Washington, Sheriff Frank Rogers, one person died attempting to protect his home from the flames.
Authorities arrested two people over the weekend on suspicion of arson, the sheriff said. They set backfires to protect their property.
More than 150 structures have been lost. The sheriff expects that number to go up.
"I've been here 30 years, never seen anything like this," Rogers said.
According to Connolly, firefighters from across the United States, including Mississippi, Illinois, New Mexico, Utah and Montana, have joined the battle, bringing to 8,928 the number of people involved in trying to contain the fires. There are 35 "hot shot" crews involved, she said.
Health officials in Washington and Idaho are warning residents that smoke drifting eastward from the Washington wildfires would create unhealthy air.
"The biggest health threat comes from the fine particles in smoke," the National Weather Service said. "These can cause burning eyes, runny nose, bronchitis and other illnesses. Smokey air can also aggravate heart and lung disease, and even lead to death."
CNN's Dave Alsup and Janet DiGiacomo contributed to this report.