Cladding on 34 tower blocks in 17 council areas in England has failed fire safety tests, the government says.
Members of the emergency services work on the middle floors of the charred remains of the Grenfell Tower block. Photo: AFP
The results mean every sample has failed the tests so far. The government plans to test up to 600 blocks.
The announcement came as the Metropolitan Police said the Grenfell Tower fire, started in a fridge-freezer, and outside cladding and insulation failed safety tests.
That fire is feared to have killed 79 people.
Camden has become the first authority to evacuate residents over concerns, asking those living in four buildings to leave.
The council said it had no option but to move residents of 650 flats on the Chalcots estate while work takes place.
Communities Secretary Sajid Javid said the residents had shown "calm and stoicism".
But he said cladding itself was not dangerous and a test failure did not necessarily mean a building would have to be evacuated.
Camden's decision to evacuate was because the failed testing of external cladding was "compounded by multiple other fire safety failures", said Mr Javid.
The testing of potentially combustible cladding "is running around the clock" and interim safety measures were being put in place for all affected buildings, he added.
The Department for Communities and Local Government (DCLG) pointed out that local authorities had been asked to prioritise buildings they had most concern over.
The DCLG's testing programme, which began on Wednesday, is able to test 100 samples a day. If needed, further lab capability could be provided.
Prime Minister Theresa May said "necessary" steps would be taken to find people evacuated from the Chalcots Estate.
Mrs May said: "We are making sure that the authority has the ability to do what is necessary to ensure people have somewhere to stay and that the work is done so that those tower blocks will become safe for them to return to in future."
The Local Government Association said some councils had introduced 24-hour a day warden patrols, to mitigate the risk before cladding is removed.
"Anyone living in a high-rise building can be reassured that their council will act on any advice from the fire service to ensure their safety," a spokesman said.
Other high-rise buildings, such as some used by the NHS, are also being tested.
Earlier, Camden council's Labour leader, Georgia Gould, said the authority had acted "as swiftly as we possibly can" to ensure people's safety.
Ms Gould said the fire service "told us they could not guarantee our residents' safety in those blocks".
"I know it's difficult, but Grenfell changes everything and I just don't believe we can take any risk with our residents' safety and I have to put them first.
"I offered to pay for fire stations to be stationed outside all of those blocks so we could have a couple of days to get the work done but the message was there was absolutely nothing I could do to make those blocks safe that night."
She said that if people still choose to not leave their homes then it would "become a matter for the fire services".
The Chalcots estate's cladding is similar to that used on the Grenfell Tower in west London.
Chalcots was refurbished between 2006 and 2009 by the same firm, Rydon, that oversaw work at Grenfell Tower in 2015-16.
Camden Council said it would remove external thermal cladding from five tower blocks on the Chalcots estate.
It also said there were concerns about the insulation of gas pipes going into flats, and fire doors.