At 12:54 a.m. London time, a fire was reported at Grenfell Tower on the Lancaster West state in North Kensington.
Prime Minister Theresa May has promised a "proper investigation" after the fire tore through the 24-storey building early on Wednesday morning amid growing concerns about how the fire could have spread so rapidly.
Following recent terrorist attacks in Manchester and London, the United Kingdom was again confronted by scenes of horror Wednesday as an apartment building became engulfed in flames with residents trapped inside.
Resident Michael Paramasivan toldBBC radio he had spoken to a woman who lived on the 21st floor: "She has got six kids".
Ashin Sha, who was with his aunt on the second floor, told the Evening Standard that residents were luckily awoken by Muslims observing Ramadan - after the smoke alarms inside the building failed to go off.
It led to scenes of sheer terror, as some occupants, a number of them in flames, leaped to certain death to escape the scorching flames. She said, they tell us to stay in. "This is a multi-ethnic, multicultural, diverse community that just didn't get served by the people representing them".
She added: "She wrapped the child up in some sort of thick blanket, and then just dropped the baby out of the window".
Some witness reports say children and a baby were seen being thrown out of windows amid the blaze.
"Somebody did, a gentleman ran forward and managed to grab the baby", she said.
"We saw the people screaming", she said. "Within another 15 minutes the whole thing was up in flames and there were still people at their windows shouting 'Help me.' You could see the fire going into their houses and engulfing the last room that they were in".
Reuters was unable to verify the witness accounts.
Investigators were still to determine the exact cause of the fire, but there have been reports that the building's cladding - two sheets of aluminium with a flammable low-density core - might have helped the fire spread externally.
Confirming the deaths, Commander Stuart Cundy, of the Metropolitan Police, said: "I can confirm twelve fatalities at this time but this figure is likely to rise during what will be a complex recovery operation over a number of days".
He said residents had complained for years about mismanagement of the block, saying he had warned that "one day there will be a catastrophic fire and that will hold these people to account".
At least 12 people have died in the tragedy, with hospitals across the capital treating 78 people, of whom 18 are in critical care.
Hundreds of firefighters tackled the blaze, rescuing 65 people, but more than 70 have been left in hospital. The housing block, built in 1974, was recently upgraded, with work finishing in May 2016, according to the Royal Borough of Kensington and Chelsea.