LONDON - An estimated 600 buildings across England could have flammable exterior panels similar to those believed linked to the deadly fire that quickly engulfed a London apartment tower last week, a Downing Street spokeswoman said Thursday.

The findings are part of an investigation into the fast-moving inferno at the Grenfell Tower, which claimed at least 79 lives and raised questions about whether the building's outside coverings, known as cladding, could have contributed to the blaze.

British Prime Minister Theresa May said that as a precaution, the cladding in similar tower blocks was being tested. Britain has around 4,000 similar high-rise apartment blocks across the country.

A report from local councils, which administer many housing developments, found around 600 "high-rise buildings could have similar cladding," a spokeswoman said.

"They are taking samples from the buildings and sending them to government testing facilities," added the spokeswoman, who did not give her name according to customary briefing rules.

Speaking to the House of Commons, May said fire officials have been told of the report and "are taking all possible steps to ensure buildings are safe and to inform affected residents."

"We cannot and will not allow people to live in unsafe homes," she said.

British media outlets have reported that the cladding on Grenfell Tower - added during a major renovation last year - was aluminum composite cladding that has a plastic core.

This model of cladding, which covered the exterior of the building, reportedly cost about 5,000 pounds ($6,300) less than a more fire-resistant version.

The Downing Street spokeswoman said that samples from the 600 buildings needed to be tested, and that the testing facility can handle about 100 samples a day. So far, three have been found to have combustible cladding in England.

It was also unclear how many people this could impact and whether the residents who live in these tower blocks will be moved. Many of the buildings are massive. The 24-story Grenfell Tower housed about 600 people.

When asked if the cladding on Grenfell Tower was compliant with Britain's building regulations for a building of Grenfell's height, May said that an investigation was underway and that the police and fire services would make a relevant statement later this week.

She said Grenfell residents will be moved to new housing within three weeks, and she added that no immigration checks will be carried out on the residents.

London's Metropolitan Police has opened a criminal investigation into the blaze that could result in prosecutions for those deemed responsible.

"For any guilty parties there will be nowhere to hide," May told lawmakers.

May has come under heavy criticism for her initial response to the tragedy when she failed to meet survivors on the day of the disaster.

On Wednesday, she said that the initial support on the ground was "not good enough" and "as prime minister, I apologize for that."

Her statement follows the resignation of the chief executive of the council that runs the borough where Grenfell fire took place.

Nicholas Holgate, chief executive of the Kensington and Chelsea council, left his post after the council came under intense criticism for alleged failings before and after the fire.