Hundreds of firefighters continued to battle large wildfires Friday in the US state of Oregon as they threatened to merge near the suburbs of Portland, the state's largest city.

Oregon governor Kate Brown said during a Friday press conference that fires have burned more than 1,500 square miles (just under 3,900 square kilometers) in the state in just the past three days, nearly double that of a typical year in the northwestern US state. Brown also noted there were dozens of people missing due to the fires, primarily in Jackson county in the south of the state and Marion county, which includes the state capital Salem. 

More than 40,000 have been evacuated to safety, according to Brown. Some evacuees are staying in the convention center in Portland. Though there have only been four confirmed deaths so far, the state's emergency management director, Andrew Phelps, said officials were "preparing for a mass fatality event."

Weather turning in firefighters' favor

The Department of Forestry Fire Chief Doug Grafe said during Friday's press conference that weather conditions were improving for the firefighters.

"We are currently in a westerly flow from the ocean. That brings lower temperatures… It'll put us in a position to move from just life safety to offense against these fires," said Grafe.

Increased humidity and calmer winds reduce the spread of wildfires and makes them easier to contain.

"The weather system fueling these fires over the past few days has finally broken down, and our firefighting teams tell me they can feel it," said Brown.

However, she said the air quality was the worst in the world at the moment due to the fires.

Fighting not just fires, misinformation

Officials also decried speculation about who might have been responsible for the fires. Rumors spreading on social media blamed far left and far right groups, including Antifa and the Proud Boys, respectively.

The FBI's Portland division tweeted Friday that it investigated several claims and found them untrue.

In neighboring Washington state, the Mason County Sheriffs Office said in a Facebook post Thursday night that people should not spread rumors as to how the fires started.

"Though some agencies have made arrests related to arson recently, they appear to all be separate individuals, however as with many incidents, it will be an ongoing investigation in each jurisdiction," read the Facebook post.

It is not clear how all of the fires in Oregon and Washington state began. California is also experiencing a harsh fire season, with more than two million acres (more than 809,000 hectares) of land destroyed by fires up and down the state.

kbd/dj (AP, AFP, dpa)