Kirk Johnsonc.2018 New York Times News Service

A sudden, fast-moving fire in Northern California forced a scramble of evacuations and road closings, burning at least 18,000 acres since early Thursday near Chico, about 100 miles north of Sacramento.

By midafternoon, the acting governor, Gavin Newsom, had declared a state of emergency, and hundreds of firefighters were on the scene or en route, said a spokeswoman for the California Department of Forestry and Fire Protection, Lynne Tolmachoff.

The blaze, named Campfire, burned through Paradise, a town of about 26,000, where a hospital was evacuated and traffic gridlock forced some people to flee vehicles on foot, according to a report on Wildfire Today, a website that covers fire news across the country.

Tolmachoff said that “numerous structures” in Butte County had burned and that some civilians and firefighters had been injured, but that there were no confirmed fatalities.

More than 23,000 people across the county of 230,000 residents were told to evacuate through an automated notification system at the Butte County Sheriff’s Office, but a spokeswoman for the sheriff said there were no firm numbers of how many had done so.

The California Department of Forestry and Fire Protection, better known as CalFire, said on its website that the fire began early Thursday near the town of Pulga, which is on the western edge of the Plumas National Forest.

“The blaze is being driven by fairly strong winds,” Rick Carhart, a CalFire spokesman, told The Associated Press. “It’s really dry and we have low humidity — and unfortunately those are great conditions for a fire to spread.”

Shelters opened in Chico, Oroville and Gridley with capacity to take nearly 2,500 people.

A red flag warning was issued by the state for a wide area of the county, as strong winds, gusting to 35 mph, and low relative humidity were elevating fire conditions, but Tolmachoff said winds were expected to ease by Friday morning.

She said the fire was moving toward the southern part of Chico, the county’s largest city, with about 93,000 people, but that a less volatile mix of fuels in the fire’s path was expected to slow its advance.

The 100-bed hospital in Paradise, Adventist Health Feather River, was closed, with all patients evacuated to hospitals in Chico and Oroville, the hospital said on its website.

Strike teams of firefighters from as far away as Oakland and Sacramento were sent to help fight the fire, and Butte College, in Oroville, closed so it could be used as a staging area for fire personnel.