(CNN) — Seven western states are under air quality alerts due to raging wildfires, which have forced thousands to evacuate and destroyed hundreds of homes.

The 92 large wildfires currently burning in the US have scorched more than 2.5 million acres, according to the National Interagency Fire Center, and their smoke has put thousands under poor air quality alerts.

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Areas of California, Nevada, Oregon, Colorado, Wyoming, Idaho and Montana are under air quality alerts Wednesday, according to the National Weather Service (NWS).

Thick smoke blanketed the resort communities of Lake Tahoe this week as the Caldor Fire burning east of Sacramento, California, continued to swell.

And in Reno, Nevada, residents were encouraged to stay indoors due to historically bad air quality.

Nevada’s Washoe County — home to Reno — saw its poorest air quality on record two days in a row, county health officials said Tuesday. The average air quality index for fine particles reached 251 Sunday, which is considered “very unhealthy,” and on Monday, the index number jumped to 291, the Washoe County Health District said.

Smoke from the fires is expected to remain a problem for the area, CNN meteorologist Michael Guy said, as it lingers specifically in portions of the Intermountain West, southern Oregon and the Great Basin, which includes areas of western Nevada.

“For the rest of this week, it looks like smoke will continue to be a problem for portions of the West,” Guy said. “Another storm system will approach the Pacific Northwest during the day, allowing winds to shift and some areas to clear. However, smoke remains to be an issue across the region as the general weather pattern does not look to change through the beginning of next week.”

For those in Oregon, the NWS advised they stay inside with windows closed when smoke levels are high.

“Wildfires burning in the region combined with forecast conditions will cause air quality levels to fluctuate and could be at unhealthy levels,” the NWS wrote in its Oregon alert.

One of the most concerning fires for firefighters is the Caldor Fire in El Dorado County, California.

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The 11-day-old fire has swept through 122,980 acres, and was 11% contained as of Tuesday evening, according to Cal Fire. The massive fire has so far destroyed 461 residences and 11 commercial properties, Cal Fire said.

California fire is nation’s top firefighting priority

Officials previously called the Caldor Fire’s behavior “unprecedented,” and now they’re worried about how it will move in the coming days.

The fire is threatening to move into the populated region of the Lake Tahoe Basin, making it country’s top firefighting priority, Chief Thom Porter of the California Department of Forestry and Fire Prevention said Monday.

“I personally don’t believe the fire is going to get into the basin proper,” Porter said of Lake Tahoe, “but I could be born wrong by that. The weather has outstripped and Mother Nature has taken over and taken fires like the Dixie to places that I never thought was possible.”

President Joe Biden on Tuesday approved California Gov. Gavin Newsom’s request for a presidential disaster declaration, which allows for additional federal resources to help support the state’s emergency firefighting efforts, the governor’s office said in a news release.

The federal aid will go toward communities in Lassen, Nevada, Placer and Plumas counties affected by the Dixie and River fires, the governor’s office said. The aid can support medical services, housing assistance and legal services as well as response and recovery costs.

As of Tuesday night, a total of 37,282 people are evacuated statewide due to wildfires, Newsom’s office said.

California’s wildfire season this year has been devastating, scorching more than 1.59 million acres so far — and that number will only go up as fires continue to grow.

The Dixie Fire — the second-largest fire in state history — which has been burning for more than a month, has grown so large that its perimeter stretches more than 500 square miles. That blaze has swelled to 733,475 acres and is 43% contained, according to Cal Fire.

Officials have warned that people should be ready to evacuate quickly if it becomes necessary.

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