LONDON — At least 11 buildings in Britain are clad in combustible material of a kind similar to the cladding that was used on the exterior of Grenfell Tower, the apartment building destroyed in London’s deadliest fire in decades, officials said on Thursday, as they scrambled to conduct safety checks on at least 600 other high-rise buildings.

Exterior cladding is thought to have contributed to the rapid spread of the fire, which consumed the 24-story Grenfell Tower in West London in just one hour, early on June 14. The fire killed at least 79 people and left hundreds of survivors homeless.

The cladding on the building — sheets of aluminum composite material, encasing a flammable polyethylene insulation — has been associated with high-rise fires in other countries and its use is restricted in the United States and elsewhere. It was permitted under British regulations, even though safety experts have long warned the metal sheets could melt under intense heat, allowing a blaze to race through the combustible material between them.

Over the weekend, the government ordered the local authorities to review records on residential buildings that are more than 18 meters (about 60 feet) in height and are clad with “aluminum-type panels.”

“Shortly before I came to this chamber, I was informed that a number of tests have come back as combustible,” Prime Minister Theresa May told lawmakers on Thursday morning. “The relevant local authorities and local fire services have been informed, and as I speak, they are taking all possible steps to ensure buildings are safe, and to inform affected residents.”

The announcement startled some members of Parliament, several of whom peppered Mrs. May with critical questions. Shortly after, Mrs. May’s aides told journalists that 600 buildings in England contained combustible material “similar” to the kind used on Grenfell Tower.

As news spread, however, Mrs. May’s office issued a clarification — saying that the 600 referred to the total number of buildings that were being subjected to safety tests after the review.

By late afternoon, Mrs. May’s office said, officials concluded that seven buildings so far had been shown to contain combustible cladding. They emphasized that samples were being tested at a rate of 100 a day and that the number of buildings at risk could grow.

Later the figures were updated in a letter from Sajid Javid, secretary of state for communities and local government, which said that “so far we have had samples from 11 high-rise buildings in eight local authority areas where the cladding has failed the test.”

It continued, “All landlords and fire and rescue services for those local authorities have been alerted to the results and we are in touch with all these areas to support and monitor follow-up action.”

The cladding at Grenfell Tower was installed as part of a renovation that was completed in May 2016.

The government did not identify the 11 buildings with combustible cladding, but the London borough of Camden announced on Thursday that the same contractor and cladding supplier involved in the Grenfell Tower renovation had also worked on the refurbishment of another complex, the 717-unit Chalcots Estate in Swiss Cottage, in northwest London.

The aluminum cladding panels “were not to the standard that we had commissioned,” the borough said in a statement, adding that it was considering legal action.

Camden officials emphasized that the Chalcots Estate had “fire-resistant rock wool insulation” and “fire-resistant sealant between floors,” which helped contain a fire in 2012, but said that they would “immediately begin preparing to remove” cladding panels from five towers in the complex.

Residents there were not comforted.

Justin Walker, 51, who has lived in the estate’s Blashford tower for 12 years, said the news had left him anxious. “It has caused sleepless nights,” he said.

Amal Salah, 45, a care worker who lives in the nearby Dorney tower with her husband and four children, said that residents frequently discussed the cladding. “Whenever we meet downstairs, it is all we talk about,” she said. “We only have one exit route besides the elevators, which you can’t use in a fire. We only have the main staircase. So we just hope that nothing will happen.”

Shohre Hosseany, 43, an immigrant from Iran who has lived in London for five years, three of them in the nearby Taplow tower, said she had “cried a lot” for the victims of the Grenfell Tower fire. She said she worried that if a fire broke out, she would be unable to escape from her 12th-floor home.

“I have arthritis and pains in my back, so if this happened here, I would die,” she said.

Notably, Mrs. May did not repeat an assertion over the weekend by two of her ministers, including Philip Hammond, chancellor of the Exchequer, that the kind of cladding used on the tower was illegal under British regulations.

If the cladding were illegal, that would deflect responsibility for the disaster away from the government and toward the tower’s owners and building contractors, but a close examination of the regulations does not support the ministers’ assertions.

The fire has created a political crisis for Mrs. May’s government, which on Sunday took control of the emergency response, sidelining officials from the local council, the Royal Borough of Kensington and Chelsea, which owns the building and was heavily criticized for a lethargic response to the catastrophe. The council’s chief executive, Nicholas Holgate, was forced out on Thursday.

Mrs. May said Thursday that within days she would appoint a judge to lead an independent public inquiry. The Metropolitan Police has opened a criminal one.

Grenfell Tower contained about 120 apartments, but Mrs. May said on Thursday that 151 homes had been destroyed, because the fire had spread beyond the tower.

The blaze turned the tower, in the North Kensington neighborhood, into a block of ash. Residents of other tall buildings in the area said the latest news had only deepened their worries.

“We’ve barely been able to sleep since the fire,” said Lindsey Harper, who lives in an eight-story building in North Kensington. “My father is in a wheelchair and we live on the fifth floor of our building. The lift rarely works. If there was a fire, there is only one tiny staircase to escape. How would we get him out?”

A resident group at Grenfell Tower had warned for years about fire hazards there, and complained that the Kensington council had ignored their warnings.

“Working-class people’s voices are ignored, their concerns dismissed, by those in power,” said Jeremy Corbyn, the leader of the opposition Labour Party. “The Grenfell Tower residents and North Kensington community deserve answers, and thousands of people living in tower blocks around the country need urgent reassurance.”

He said that local councils had reduced fire inspections because of budget cuts, and that combustible cladding needed to be removed from all buildings where it had been installed, whatever the cost.