Oregon governor Kate Brown said a change of weather could bring respite for US firefighters battling deadly blazes Friday — while clarifying a previous assertion by state officials that half a million people had been evacuated from the fire’s path.

More than 40,000 Oregonians have fled their homes so far, said Brown, with some 500,000 still under evacuation warnings.

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The warnings range from packing valuables and monitoring the situation, to immediate departure.

Well over a million acres of land has burned in the northwestern state, with three reported dead, and dozens still unaccounted for.

But “unprecedented” weather conditions earlier in the week including strong, dry east winds and soaring temperatures have begun to ease.

“The weather system fuelling these fires over the past few days has finally broken down,” Brown told a press conference.

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“We anticipate cooler air and moisture coming in the next few days, which is really good news,” she added.

But under the expected conditions, heavy smoke could restrict the use of firefighting aircraft, officials warned.

Earlier in the week, Brown warned that Oregon could expect to see a “great deal of loss, both in structures and in human lives,” with at least five towns “substantially destroyed.”

On Friday, she added: “As of now, there are early reports from our state police that there are dozens of missing persons related to the fires, specifically in Jackson, Lane and Marion counties.”

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More than 20,000 firefighters from across the US are battling wildfires up and down the West Coast, with 16 deaths so far this week and wide stretches of California, Oregon and Washington still cut off by flames.