LONDON — At least six deaths were confirmed early Wednesday after a blaze ripped through a high-rise apartment block in the British capital as residents slept. At least 50 people were injured, according to authorities.

More than 250 firefighters battled the inferno at Grenfell Tower in west London through the night.

Local resident Tim Downie told NBC News he saw “people dangling children out the windows to try and get them to safety” as flames spread upward. Another witness recounted watching someone jumping from it.

Local officials believe that several hundred people were in the building, which dates back to the 1970s. The high-rise had a “stay put” policy in the event of a fire — with residents urged to shut their windows and doors and await rescue.

London Fire Brigade Commissioner Dany Cotton called it an “unprecedented incident,” adding that a “number of fatalities” had been confirmed. Police later put the death toll at 6, but warned that figure was likely to grow,

“In my 29 years of being a firefighter, I have never, ever seen anything of this scale,” Cotton said. “This is a major fire that’s affected all floors of the 24-story structure from the second floor upwards.”

She highlighted that “very large numbers” were rescued by emergency crews early on. But almost nine hours after the blaze broke out, Cotton admitted “we have absolutely no idea” how many people remained unaccounted for.

Michael Paramasivan was wearing only underwear and a robe when he fled the seventh floor about 35 minutes after the blaze was reported.

He described the scene in the stairwell as an “absolute horror story.”

“There was smoke everywhere, people screaming and shouting,” the 37-year-old told NBC News. “It all happened so fast but was really, really frightening. I’m shaking.”

He added: “They say you’re supposed to put a towel under the door and wait for rescue but I wasn’t going to hang around … There was some kind of alarm but it was barely audible. It certainly wouldn’t have woken you up.”