Shocking pictures and videos posted on Twitter show the flats are fully ablaze, with flames ripping through the entire building at De Pass Gardens in Barking in the United Kingdom capital.
Comments posted online by local residents suggest the flats have only just been built, although this has not been confirmed.
Nearly two years ago, Grenfell Tower, a high-rise social housing block in west London, was engulfed by flames in the middle of the night, killing 71 people in the country's deadliest domestic fire since World War Two.
Firefighters are set to carry out an extensive investigation into the cause of the blaze that destroyed 20 flats in Barking..
London Fire Brigade's Andy Maloney said: "Crews are continuing to work really hard at the scene to bring the fire under control".
They added: "The Brigade was called at 3:31pm and is still at the scene".
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London Mayor Sadiq Khan said the "shocking" fire could have "easily resulted in fatalities".
Families living in Samuel Garside House, where two-bedroom flats sold for £300,000, said the fire alarm and sprinkler system had not been working for four months. "But we are helpless".
Around 1:30 p.m. ET, the London Fire Brigade announced the fire was under control.
"I live nearby so I went to the building to help get people out", Mr Boff said.
There were no reports of any injuries at the time of this report, according to authorities.