An estimated 600 buildings in England have cladding similar to that used at the Grenfell Tower block where a devastating blaze killed at least 79 people, a spokeswoman for Prime Minister Theresa May said on Thursday.
"The estimate provided to us by councils is that there are approximately 600 high rise buildings with similar cladding," the spokeswoman said.
"We are obviously in touch with all the local authorities to encourage them to urgently send us the samples and then we will carry out the checks that we need," she said.
She added that cladding on three buildings has so far tested positive as combustible. The estimate does not include buildings in Scotland, Wales and Northern Ireland.
Downing street later confirmed seven block of flats in four local authority areas were found to have flammable facades, with tests being conducted urgently to see if many more could have the same material.
Flames spread rapidly up the 24-storey residential tower block last week, trapping people inside, in what was Britain's worst blaze since World War Two. Exterior cladding added during a refurbishment may have played a part, residents have said.
The disaster heaped pressure on Prime Minister Theresa May, already fighting for her political survival after a snap election saw her party lose its parliamentary majority. It has acted as a focal point for anger at government cuts to local authority funding and drawn accusations of criminal negligence.
"(We) should of course be careful on speculating what caused this fire, but as a precaution the government has arranged to test cladding on all relevant tower blocks," May told parliament.
"Shortly before I came to the chamber, I was informed that a number of these tests have come back as combustible."
She said local authorities and fire services had been informed and were taking steps to make affected buildings safe and to inform residents.
May has launched a public inquiry into the fire and police have announced a criminal investigation.
May said tests on the cladding of Grenfell Tower where the fire blazed would be made public in the next 48 hours.
"This has been a wake-up call for the whole country," said Jeremy Corbyn, leader of the opposition Labour Party.
"Residents of tower blocks all over the country are concerned, worried and frightened for their own safety. What we need is a step change in our attitude towards housing in this country."
After apologising for a slow state response to the fire, May said it was right that the head of the local council had resigned. Nicholas Holgate, chief executive of Kensington and Chelsea council, said he was forced out by the government.
