Thousands of people were evacuated in Northern California overnight, as yet another rapidly growing wildfire raged, joining hundreds of blazes in the Pacific Northwest and Canada that are sending smoke across swaths of the region, fire officials and weather services said.

The Park Fire in Butte County, California, exploded overnight from about 1,400 acres on Wednesday to about 45,500 acres today, according to the California Department of Forestry and Fire Protection, or Cal Fire.

It’s burning in California’s Central Valley about 80 miles north of the state capital Sacramento, and was only 3 percent contained this morning, said Cal Fire public information officer Dan Collins. No injuries were reported. Thousands were ordered to leave their homes.

“We have 400 firefighters and personnel on the scene, but we have units headed our way from all across the state,” Collins said. “The help is needed.”

More than 4,000 people were evacuated in Butte County and the city of Chico, said Megan McMann a spokesperson for the Butte County Sheriff’s Office.

“Evacuations are ongoing as the fire grows,” she said. “We had assistance from 10 different law enforcement and fire agencies. More are on the way today.”

The largest fire now burning in the United States, Oregon’s Durkee Fire, has burned at least 240,000 acres, threatened multiple small towns, scorched ranch land and killed cattle by the hundreds, local media reports said.

High winds, with gusts of 60 mph along with lightning strikes Wednesday and overnight could fan the flames, said Marc Chenard, a forecaster with the National Weather Service in College Park, Maryland.

The fire, about 100 miles northwest of Boise, Idaho, was zero percent contained this morning. More wind was forecast and lightning was possible.

“There is zero percent chance of rain in the forecast for the region,” Chenard said.

Smoke from fires in western Canada and the Pacific Northwest is blamed for hazy skies and bad air from the Rocky Mountains to Chicago, weather reports said. Denver had the worst air quality in the U.S. and ranked the 22nd worst in the world, according to IQAir, a group that tracks air pollution across the globe.

The air could be clearing later today as a high-pressure ridge rolls in bringing clearer skies, according to weather reports.

Scientists and environmental advocates have long called for global leaders to phase out and end the reliance on fossil fuels to prevent catastrophic effects of climate change, including worsening wildfires.