Fire and rescue crews are fighting a blaze and searching for people who may have been trapped in a 24-story apartment building in London that was engulfed in fire overnight. At least six people have died from the fire, which was not yet fully under control nearly 12 hours after it started."These are very early stages and we do expect that figure to rise," London's Metropolitan Police said of the death toll.The blaze at Grenfell Tower was reported around 1 a.m. (8 p.m. ET Tuesday). Soon after, people nearby reported seeing smoke and flames shooting from its windows. Since then, more than 64 people have been taken to hospitals, and 20 are in critical care units, the London Ambulance Service says."This is an unprecedented situation, with a major fire that has affected all floors of this 24 story building, from the second floor up," said London Fire Commissioner Dany Cotton.Cotton told reporters she'd never seen anything like the fire in her nearly 30 years as a firefighter. More than 200 firefighters have been called in, the London Fire Brigade says.Up to 600 people may have been inside the building's 120 apartments at the time the blaze broke out.The Telegraph reports: Residents who escaped spoke of others trapped and screaming for help, with some holding children from windows and others jumping from upper floors. Some were reported to have attempted to use bin bags as makeshift parachutes.One person, who did not want to be identified, told the British newspaper The Guardian, "I'm lucky to be alive — and lots of people have not got out of the building."Police say it will take some time to confirm the cause of the fire. Residents said the blaze appeared to start in an apartment on a lower floor and spread upward quickly.As noon approached Wednesday, the building in the west London neighborhood of North Kensington was still smoldering and breaking out into flames. Volunteers were bringing sandwiches to people forced out of their homes; others donated supplies and money.The Associated Press reports that the building had been viewed as a fire risk: "Local residents said they had warned local authorities about fire issues in the building, a public housing block built in 1974 and containing 120 homes, according to the Royal Borough of Kensington and Chelsea. " 'We've complained to council,' said Edward Daffarn, 55, who said nothing had been done to improve safety. 'I consider this mass murder.' "On Twitter, London Mayor Sadiq Khan said the fire was declared a major incident; he and other city officials are spreading information about how survivors and families can find one another or report someone missing. Copyright 2017 NPR. To see more, visit http://www.npr.org/.