iStock/Thinkstock(LONDON) — A massive fire engulfed a residential high-rise building in London on Wednesday, leaving scores injured and at least six people dead.

The London Fire Brigade dispatched at least 40 fire engines, 20 ambulance crews and more than 200 firefighters in an effort to battle the conflagration at the 24-story Grenfell Tower in West London.

The Metropolitan Police said late Wednesday morning that at least six people had been killed, a number they expected to increase.

“I can confirm six fatalities at this time but this figure is likely to rise during what will be a complex recovery operation over a number of days. Many others are receiving medical care,” said Commander Stuart Cundy.

Authorities said they were still monitoring the stability of the structure, but firefighters had managed to enter the building and had checked as many as 20 floors for remaining people.

“This is an unprecedented incident,” London Fire Commissioner Dany Cotton told reporters.

“In my 29 years of being a firefighter, I have never ever seen anything of this scale.”

An exact figure for the number of injured has not yet been released either, but the London Ambulance Service said 50 people had been transported to five local hospitals after the incident, while the London Metropolitan Police said in a prior statement many people were being given medical care for a range of injuries.

It is not known yet what caused the fire, which firefighters continue to battle.

The blaze has left the building almost totally charred, and there were fears in the morning about the building’s structural integrity as it appeared to lurch slightly to one side.

The tower, built in 1974, contains 120 apartments, according to its management company Kensington and Chelsea Tenant Management Organisation.

 One resident told ABC News that he woke up, smelling smoke, and thought his laptop was overheating. He said it seemed as if the fire had been going off for at least 30 minutes before the building’s fire alarms went off.

The resident, who said he was initially told to stay in place, said he fled the building once he realized how thick the smoke was. Regrettably, he said he was unable to carry his elderly father and fears that he may not have survived.

London Fire Brigade assistant commissioner Dan Daly said in a statement that “firefighters wearing breathing apparatus are working extremely hard in very difficult conditions to tackle this fire. This is a large and very serious incident and we have deployed numerous resources and specialist appliances.”

London Mayor Sadiq Khan said he was “truly devastated” by the incident and warned that the numbers of dead and injured could increase.

“My heart goes out to everyone affected. I am sad to confirm that we now know there have been fatalities and more than fifty people have been taken to hospitals [around London],” Khan said in a statement early Wednesday. “The fire service is dealing with a rapidly changing situation and these numbers [of dead and injured] are likely to rise.”

London Metropolitan Police said they were called at 1:16 a.m. “to reports of a large fire at a block of flats in the Lancaster West Estate, W11.”

Social media users posted images and video of the fire as it continued to rage after sunrise, while others posted images of loved ones who had gone missing after the fire.

 “It looks very bad, very very bad. I’ve never seen anything like this. It’s just such a big fire,” Tim Downey, an eyewitness, told BBC early Wednesday. “It has burned through to its very core.”

He said part of the building appeared to be “completely burned away.”

“The whole building is just crumbling. It’s just billowing black smoke,” Downey said.

 Another witness, who only gave her first name, Hanan, told ABC News that she managed to escape from the building’s ninth floor, but she said was worried about her brother, Abdul Aziz, and his family who were on the 26th floor.

Some tenants have complained about the upkeep of the tower in the past, specifically warning about the fire risk. In November, a residents group called Grenfell Action Group said that only a “catastrophic event” would expose the concerns they had about the building’s landlord, according to the group’s blog post.

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