Seattle had the worst air quality in the world for the second day in a row Thursday as the Pacific Northwest air continued to be clogged with smoke from multiple wildfires in the region.

The air quality in Seattle was ranked worst worldwide on Wednesday, according to IQAir, a Swiss air quality technology company that monitors real-time air quality. A heavy fog of smoke covered the city again Thursday as the air quality index remained at a “very unhealthy” level for all groups.

Portland, Oregon, and Vancouver, British Columbia, have also ranked among the world’s worst locations for air quality over the past two days, alongside cities in Pakistan, China and India. By Thursday afternoon, Portland was the second worst in the world, according to IQAir.

“There’s widespread smoke that we’ve been seeing now for quite some time,” Dev McMillian, a National Weather Service meteorologist, told USA TODAY on Wednesday.

The weather service and the Puget Sound Clean Air Agency both warned residents in the Seattle area of diminished air quality due to wildfire smoke that is forecast to remain problematic into Friday. The agencies advised people to limit outdoor exposure and keep indoor air clean by closing windows and doors.

Multiple cities in Oregon, including the Portland metropolitan areaand south to Eugene, were also contending with air quality in the unhealthy to unhealthy for sensitive groups range, according to IQAir. 

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Smoke from the Nakia Creek Fire clogs the air on Wednesday near Camas, Washington, a few miles north of the state's border with Oregon.

Nine fires were burning in Washington state and Oregon before the NWS issued a red flag warning for critical fire conditions last weekend. The Nakia Creek Fire in southwest Washington exploded in size on Sunday, engulfing the region with smoky air.

Unhealthy air quality and exposure to wildfire smoke puts sensitive groups at risk, including outdoor workers, pregnant people, people with heart and lung disease and those over the ages of 65 or under the age of 18, according to the U.S. Environmental Protection Agency.

Conditions were expected to improve late Thursday due to rainfall and cooler temperatures, McMillian said.

“We’re gonna see a first decent shot of rain since early June this year and much cooler temperatures,” McMillian said. “We’re gonna see values, I believe, on Friday, around 60 before falling to the 50s for the remainder of the weekend.”

Contributing: The Associated Press