The second-largest wildfire on record in Texas raged across 850,000 acres on Wednesday, as firefighters from around the state tried to contain it. The blaze has consumed houses, burned vast ranch lands, killed livestock and forced evacuations across the sparsely populated Texas Panhandle.

The blaze, known as the Smokehouse Creek fire, ignited on Monday and by Wednesday had spread across vast swaths of ranch lands, fueled by strong winds and dry conditions. It still had not been contained and was growing, according to the Texas A&M Forest Service.

Satellite data from the National Interagency Fire Center suggested that the fire had already become the largest ever seen in the state.

The fire spread around the town of Canadian, a cattle-country community of around 2,200 people northeast of Amarillo, near the Oklahoma state line. Residents who had not already evacuated were forced to shelter in place overnight.

About 35 people, mostly residents who tried to leave but found the roads closed by the fire, took shelter in a “safe room” at the emergency operations center, said Lisa Johnson, the Hemphill County judge, who also spent the night there. Other residents huddled in a local church, the pastor there said.Some simply stayed at home and hoped for the best.

“There is a lot of stuff that’s just gone,” said Cody Cameron, 56, who said he and his wife had been at home trying to gather up their three cats when the roads into and out of Canadian were closed on Tuesday. By Wednesday, the roads had reopened, and the ground was blackened on both sides of Highway 60 for about 10 miles approaching town.

A portion of the fire got close to Mr. Cameron’s backyard during the night, he said, but then it died away. “We got lucky,” he said.

Officials said there had been no deaths or severe injuries attributed to the fire so far.

The blaze tore across ranches, overtaking cattle and forcing ranchers to try to save their own properties.

“I was out here fighting the fire two days straight,” said Jeff Chisum, whose family owns a 30,000-acre cattle ranch in Roberts County. Nearly all of the land had burned, he said, but family members were able to protect the buildings using pickup trucks with firefighters in the back. “One guy driving, one or two guys in the back, just run down the line and try to turn it away,” Mr. Chisum said of how they poured water on the flames.

Some of his roughly 600 head of cattle managed to avoid the fire; others did not. “We lost some, and there are some that we’re having to shoot that are still alive but are burnt up,” he said. “We’re in love with the animals and the country, and whenever something like this comes through and destroys it all, it’s hard to swallow.”

A spokesman for the Forest Service said about 200 firefighters were at work across the Panhandle fighting several wildfires, with most of them focused on the Smokehouse Creek blaze. High winds prevented the use of planes to try to stop the fires from spreading.

The full extent of the damage was not yet clear on Wednesday. While some houses on the outskirts of Canadian appeared to have burned, the center of town appeared largely to have been spared.

Only portions of the tan brick walls of Sheriff Brent Clapp’s house on Locust Street remained standing on Wednesday amid a pile of charred debris and white ash. He said his wife had already evacuated, and he had been out working when the fire came.

“I was heading south down Highway 83 and the fire crossed the highway behind me, and I had a gut feeling,” Sheriff Clapp of Hemphill County said. “I just knew.”

On Wednesday, as he was looking through the smoldering ruins, he found his spirits lifted when he discovered that a cement fountain in the shape of an angel, a gift from his father, had survived.

“In this community, everyone pulls together,” he said, recalling how a local resident had showed up earlier in the day, given him a hug and asked if he needed any food. “Everybody will be OK.”

While the immediate danger in Canadian had passed, the Smokehouse Creek fire raged on across the rural landscape on Wednesday. “It looks alarming, how quickly it is spreading,” said Erin O’Connor, a spokeswoman for the Forest Service. The largest wildfire ever recorded in Texas was the East Amarillo Complex fire in 2006, which scorched about a million acres.

The fire this week was fueled by dry, dead grasses in a drainage area, the “perfect environment to support the growth that we have seen,” Ms. O’Connor said.

Gov. Greg Abbott of Texas issued a disaster declaration on Tuesday for 60 counties, activating state resources to help local firefighters. He urged residents to limit activities that could create sparks.

The fires raged and erratically shifted on Tuesday as cold air with a rapid change in wind direction pushed through the region. The fire danger was expected to ease on Thursday, with lighter winds forecast across the Texas Panhandle.

“Conditions are going to moderate a little bit,” Ms. O’Connor said, which would give firefighters a chance to suppress the blazes before Friday, when the humidity is expected to drop again and strong winds are forecast to return.

In addition to the Smokehouse Creek fire, the Forest Service was tracking other active fires, including around the town of Fritch, north of Amarillo.

“This is definitely a disaster,” said Jerry Langwell, the emergency management coordinator for Hutchinson County, speaking inside a temporary shelter for residents in Fritch late on Tuesday. “The damage is bad. I would say, 50 percent of the structures between here and Borger are damaged in some way,” he added, referring to another town about 12 miles away.

A spokeswoman for Mr. Langwell said on Wednesday in a video on Facebook that residents could re-enter the town, but she warned them to be ready for a grim scene.

“I don’t think a lot of the folks that live in the Fritch area are probably going to be prepared for what they’re going to see as they pull into town,” said the spokeswoman, Deidra Thomas. “It’s kind of like you see with a tornado. It will hit one house and completely miss the next one.”

Over the state line in western Oklahoma, local officials told some residents of Ellis and Roger Mills Counties to leave.

Near Amarillo, a wildfire was burning north of the Pantex plant that disassembles nuclear weapons, officials said. The plant suspended operations on Tuesday and ordered nonessential personnel to evacuate. It reopened on Wednesday.

There was no fire on the plant’s site or near its boundaries, but nuclear safety officials were responding anyway, said Laef Pendergraft, a nuclear safety engineer for the National Nuclear Security Administration production office at Pantex. The plant has an on-site fire department, he said at a news conference.

Unseasonably high temperatures and high winds were spurring wildfires elsewhere in the Great Plains as well, including in Nebraska and Kansas.

Reporting was contributed by Christine Hauser, John Yoon, Delger Erdenesanaa and Judson Jones.