Around 600 high rises across England are using similar cladding to Grenfell Tower, Downing Street estimates.
Tower blocks across the UK are being examined after the London blaze, which left 79 people dead or missing, presumed dead.
Three samples have been shown to be “combustible” and more results will be made public in the next 48 hours.
A No 10 spokeswoman said it was a “matter of absolute urgency” to tell residents.
Theresa May said all local authorities responsible for the flats had been told.
The announcement comes after the boss of Kensington and Chelsea Council resigned after criticism of the London authority’s response.
Speaking in the Commons, Mrs May said that the council “couldn’t cope” in the aftermath of the fire, and that it “was right” its chief executive, Nicholas Holgate, had stepped down.
Councils were told to give details to the government about the cladding they used in the tower blocks by Monday.
The Department for Communities and Local Government is then co-ordinating tests on it – with up to 100 able to take place in a day.
A spokeswoman from Downing Street said: “So far, three samples have been found to be combustible.
“We are 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 to see where we are with that.”
She added: “Obviously nobody will be living in buildings that are unsafe. They will be rehoused if they need to be and landlords will be asked to provide alternative accommodation where that’s possible.”
Camden Council confirmed that cladding used on its Chalcots estate would be removed after safety tests.
Councillor Georgia Gould, leader of the council, said: “The new results from the laboratory show that the outer cladding panels themselves are made up of aluminum panels with a polyethylene core.
“Therefore, the panels that were fitted were not to the standard that we had commissioned. In light of this, we will be informing the contractor that we will be taking urgent legal advice.” -BBC
