About 600 high-rise buildings across England are being urgently tested to see if their cladding is combustible.
Cladding on the outside of London's Grenfell Tower is thought to have contributed to the rapid spread of fire through the apartment block, in which at least 79 people are believed to have died.
So far, samples from 11 residential high-rise buildings in eight local authority areas have been found to have combustible cladding, the BBC reported.
Prime Minister Theresa May told parliament some buildings have already failed.
"I was informed that a number of these tests have come back as combustible, 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."
Communities Secretary Sajid Javid has also written to all MPs saying landlords of the 11 affected buildings have been told to inform their tenants - once done, the areas could be identified to the public.
Only Camden, Manchester and Plymouth are named in his letter, which also says the Army has been assisting with building repairs.
A spokesman for the Prime Minister earlier pointed out that a failed cladding test did not necessarily mean a building was unsafe - that would depend on the amount of cladding used and where it was fitted.
Arconic, an engineering and manufacturing company, said one of its products, Reynobond PE (polyethylene) - an aluminium composite material - was "used as one component in the overall cladding system" of Grenfell Tower.
"We will fully support the authorities as they investigate this tragedy," a spokesman for the US-based firm said.
Safety concerns may go beyond housing sector
The BBC has learned that Premier Inn is "extremely concerned" about cladding on three of its hotels.
Until now, safety fears over cladding have centred on council high rises, but concerns appear to reach beyond the housing sector.
Premier Inn has told BBC Newsnight that cladding on its hotels in Maidenhead, Brentford and Tottenham did not appear to comply with government guidance for tall buildings - although it did appear to be a less flammable type than that used at Grenfell Tower.
The hotel chain said an independent expert has assured them that the hotels were safe to stay open given their "robust" safety measures including fire detectors and smoke alarms in every room.
The hotels do not operate a "stay put" policy and have multiple means of escape.
Newsnight's Chris Cook said Premier Inn was just one of a long list of places that could have fire safety issues - and were only singled out by the programme because they responded so quickly and in full to his questions.
The Department for Communities and Local Government has written to all local authority and housing association chief executives to advise them on steps to take if tower blocks in their area are found to be clad in combustible panels.
The latest test results come after the boss of Kensington and Chelsea Council resigned following criticism of the authority's response to the disaster.
Speaking in the Commons, Mrs May said the council "couldn't cope" in the aftermath, and that it "was right" its chief executive, Nicholas Holgate, had stepped down.
In the wake of the tragedy, councils were told to give details to the government about cladding used in their tower blocks by 20 June.
'They will be rehoused'
Cladding is typically fitted to the outside of high-rise buildings to improve insulation and tidy up the appearance of often ugly blocks.
Britain's Department for Communities and Local Government is now co-ordinating tests on it - with up to 100 able to take place in a day.
A Downing Street spokeswoman said no-one would be left to live in unsafe buildings.
"They will be rehoused if they need to be and landlords will be asked to provide alternative accommodation where that's possible," she said.
Earlier, there had been some confusion after Downing Street said 600 tower blocks had "similar cladding" to Grenfell Tower.
The Department for Communities and Local Government later clarified that the figure of 600 referred to the number of buildings with cladding of any kind.
- BBC / RNZ