At least five people have died and dozens are missing in Oregon as wildfires sweep through the state, burning more than a million acres and resulting in thousands of evacuations, according to media reports.

Andrew Phelps, the state's emergency management director, said officials were “preparing for a mass fatality event." In a news briefing, Gov. Kate Brown said 40,000 Oregonians have been evacuated and around 500,000 are in different levels of fire zones -- either being told to leave or to be prepared to do so.

She also said the weather had improved.

“The weather system fueling these fires over the past few days has finally broken," Brown said. "We anticipate cooler air and moisture coming in the next few days."

Reports from the Oregon State Police indicated dozens of missing people related to fires in Jackson, Lane and Marion counties, Brown said. In California, where firefighters also are battling wildfires, 10 people were reported dead. A 1-year-old also died in wildfires in Washington.

Authorities on Friday said a man had been arrested on two counts of arson and multiple counts of criminal mischief for allegedly starting a fire in Jackson County. The Jackson County Sheriff’s Office said someone saw a man later identified as Michael Jarrod Bakkela, 41, setting a fire behind a home.

The fire is believed to be related to one of two fires that merged to become the Almeda Fire.

Hundreds of firefighters are battling two other large fires -- called the Beachie Fire and the Riverside Fire -- that threatened to merge Friday near populated areas, including near Portland. The city declared a state of emergency Thursday and officials offered resources to help combat the fires.

In this Thursday Copernicus Sentinel-3 image, provided by the European Space Agency, ESA, multiple fires can be seen hovering over the U.S. states of California, Washington and Oregon. In the top of the image, the cities of Vancouver and Seattle are visible. (ESA, CC BY-SA IGO 3.0 via AP)

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The Oregon Convention Center in Portland was repurposed into a shelter to house evacuees. Smoke from the fires transformed the state's air quality, which Brown said now "ranks the worst in the world."

She said the White House approved a request from the state for an emergency declaration to help provide assistance from the Federal Emergency Management Agency.

The Associated Press contributed to this report.