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 74 people were injured, according to authorities.

More than 250 firefighters battled the west London inferno 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.

Witness Samira Lamrani said one woman wrapped a baby up "in some sort of thick blanket" and dropped the tot from around the 9th floor. "Miraculously the baby just sort of dropped in a straight line, and a guy just ran forward and the baby fell into his arms," she added.

Several others recounted watching people jumping from Grenfell Tower.

See images from the scene:

27 PHOTOS Grenfell apartment tower fire in London See Gallery Grenfell apartment tower fire in London Flames and smoke billow as firefighters deal with a serious fire in the Grenfell Tower apartment block at Latimer Road in West London, Britain June 14, 2017. REUTERS/Toby Melville TPX IMAGES OF THE DAY TOPSHOT - Fire engulfs Grenfell Tower, a residential tower block on June 14, 2017 in west London. The massive fire ripped through the 27-storey apartment block in west London in the early hours of Wednesday, trapping residents inside as 200 firefighters battled the blaze. Police and fire services attempted to evacuate the concrete block and said 'a number of people are being treated for a range of injuries', including at least two for smoke inhalation. / AFP PHOTO / Daniel LEAL-OLIVAS (Photo credit should read DANIEL LEAL-OLIVAS/AFP/Getty Images) Flames and smoke engulf Grenfell Tower, a residential block on June 14, 2017 in west London. The massive fire ripped through the 27-storey apartment block in west London in the early hours of Wednesday, trapping residents inside as 200 firefighters battled the blaze. Police and fire services attempted to evacuate the concrete block and said 'a number of people are being treated for a range of injuries', including at least two for smoke inhalation. / AFP PHOTO / Daniel LEAL-OLIVAS (Photo credit should read DANIEL LEAL-OLIVAS/AFP/Getty Images) Members of the emergency services are parked by Grenfell Tower, a residential block which was engulfed by a huge fire on June 14, 2017 in west London. The massive fire ripped through the 27-storey apartment block in west London in the early hours of Wednesday, trapping residents inside as 200 firefighters battled the blaze. Police and fire services attempted to evacuate the concrete block and said 'a number of people are being treated for a range of injuries', including at least two for smoke inhalation. / AFP PHOTO / Daniel LEAL-OLIVAS (Photo credit should read DANIEL LEAL-OLIVAS/AFP/Getty Images) Flames and smoke billow as firefighters deal with a serious fire in a tower block at Latimer Road in West London, Britain June 14, 2017. REUTERS/Toby Melville Local residents watch smoke billow from Grenfell Tower, a residential block on June 14, 2017 in west London. The massive fire ripped through the 27-storey apartment block in west London in the early hours of Wednesday, trapping residents inside as 200 firefighters battled the blaze. Police and fire services attempted to evacuate the concrete block and said 'a number of people are being treated for a range of injuries', including at least two for smoke inhalation. / AFP PHOTO / Daniel LEAL-OLIVAS (Photo credit should read DANIEL LEAL-OLIVAS/AFP/Getty Images) LONDON, ENGLAND - JUNE 14: Smoke rises after a huge fire engulfed the 24 storey residential Grenfell Tower block in Latimer Road, West London in the early hours of this morning on June 14, 2017 in London, England. The Mayor of London, Sadiq Khan, has declared the fire a major incident as more than 200 firefighters are still tackling the blaze while at least 50 people are receiving hospital treatment. (Photo by Carl Court/Getty Images) LONDON, UNITED KINGDOM - JUNE 14: A fire rages through a residential tower block, Grenfell Tower, with the entire building engulfed in flames on June 14, 2017 in Kensington, West London, England. More than 200 firefighters are attending the incident and there are reports of people trapped inside. No figures are available as to casualties. PHOTOGRAPH BY Paul Davey / Barcroft Images London-T:+44 207 033 1031 E:hello@barcroftmedia.com - New York-T:+1 212 796 2458 E:hello@barcroftusa.com - New Delhi-T:+91 11 4053 2429 E:hello@barcroftindia.com www.barcroftimages.com (Photo credit should read Paul Davey / Barcroft Images / Barcroft Media via Getty Images) LONDON, ENGLAND - JUNE 14: Smoke rises from the burning 24 storey residential Grenfell Tower block in Latimer Road, West London on June 14, 2017 in London, England. The Mayor of London, Sadiq Khan, has declared the fire a major incident as more than 200 firefighters are still tackling the blaze while at least 50 people are receiving hospital treatment. (Photo by Carl Court/Getty Images) LONDON, ENGLAND - JUNE 14: A photographer takes photos as smoke continues to rise from the building after a huge fire engulfed the 24 storey residential Grenfell Tower block in Latimer Road, West London in the early hours of this morning on June 14, 2017 in London, England. The Mayor of London, Sadiq Khan, has declared the fire a major incident as more than 200 firefighters are still tackling the blaze while at least 50 people are receiving hospital treatment. (Photo by Leon Neal/Getty Images) LONDON, ENGLAND - JUNE 14: A man looks distressed as he speaks to a fire fighter after a huge fire engulfed the 24 storey residential Grenfell Tower block in Latimer Road, West London in the early hours of this morning on June 14, 2017 in London, England. The Mayor of London, Sadiq Khan, has declared the fire a major incident as more than 200 firefighters are still tackling the blaze, while at least 50 people are receiving hospital treatment. (Photo by Leon Neal/Getty Images) LONDON, UNITED KINGDOM - JUNE 14: Evacuated residents wait o the pavement near the scene after a fire raged through a residential tower block, Grenfell Tower, with the entire building engulfed in flames on June 14, 2017 in Kensington, West London, England. More than 200 firefighters are attending the incident and there are reports of people trapped inside. No figures are available as to casualties. PHOTOGRAPH BY Paul Davey / Barcroft Images London-T:+44 207 033 1031 E:hello@barcroftmedia.com - New York-T:+1 212 796 2458 E:hello@barcroftusa.com - New Delhi-T:+91 11 4053 2429 E:hello@barcroftindia.com www.barcroftimages.com (Photo credit should read Paul Davey / Barcroft Images / Barcroft Media via Getty Images) Smoke billows from a tower block severly damaged by a serious fire, in north Kensington, West London, Britain June 14, 2017. REUTERS/Neil Hall LONDON, ENGLAND - JUNE 14: Smoke rises from the building after a huge fire engulfed the 24 storey residential Grenfell Tower block in Latimer Road, West London in the early hours of this morning on June 14, 2017 in London, England. The Mayor of London, Sadiq Khan, has declared the fire a major incident as more than 200 firefighters are still tackling the blaze while at least 50 people are receiving hospital treatment (Photo by Kate Green/Anadolu Agency/Getty Images) LONDON, ENGLAND - JUNE 14: Fire fighters tackle the building after a huge fire engulfed the 24 storey residential Grenfell Tower block in Latimer Road, West London in the early hours of this morning on June 14, 2017 in London, England. The Mayor of London, Sadiq Khan, has declared the fire a major incident as more than 200 firefighters are still tackling the blaze while at least 50 people are receiving hospital treatment. (Photo by Carl Court/Getty Images) Local residents watch as Grenfell Tower is engulfed by fire on June 14, 2017 in west London. The massive fire ripped through the 27-storey apartment block in west London in the early hours of Wednesday, trapping residents inside as 200 firefighters battled the blaze. Police and fire services attempted to evacuate the concrete block and said 'a number of people are being treated for a range of injuries', including at least two for smoke inhalation. / AFP PHOTO / Daniel LEAL-OLIVAS (Photo credit should read DANIEL LEAL-OLIVAS/AFP/Getty Images) TOPSHOT - Two men hug within the security cordon as Grenfell Tower is engulfed by fire on June 14, 2017 in west London. The massive fire ripped through the 27-storey apartment block in west London in the early hours of Wednesday, trapping residents inside as 200 firefighters battled the blaze. Police and fire services attempted to evacuate the concrete block and said 'a number of people are being treated for a range of injuries', including at least two for smoke inhalation. / AFP PHOTO / Daniel LEAL-OLIVAS (Photo credit should read DANIEL LEAL-OLIVAS/AFP/Getty Images) Firefighters stand amid debris in a childrens playground near a tower block severly damaged by a serious fire, in north Kensington, West London, Britain June 14, 2017. REUTERS/Neil Hall Two women sit on the grass after a tower block was severly damaged by a serious fire, in north Kensington, West London, Britain June 14, 2017. REUTERS/Neil Hall A firefighter directs a jet of water at a tower block severely damaged by a serious fire, in north Kensington, West London, Britain June 14, 2017. REUTERS/Neil Hall Smoke billows from a tower block severly damaged by a serious fire, in north Kensington, West London, Britain June 14, 2017. REUTERS/Toby Melville Emergency fire services tackle a blaze at Grenfell Tower near Notting Hill on 14th June 2017 in West London, United Kingdom. The huge fire engulfed the tower block, trapping many people in their homes. A number of fatalities are reported. The block of flats in the Borough of Kensington and Chelsea,ï¿½billowed large plumes of smoke way above the capital after the blaze broke out in the early hours of Wednesday morning. Londoners came out on the streets to help, offer food and water, support and assistance to those who had lost their homes or didnt know the whereabouts of their friends and family. (photo by Mike Kemp/In Pictures via Getty Images) A firefighter directs a jet of water at a tower block severely damaged by a serious fire, in north Kensington, West London, Britain June 14, 2017. REUTERS/Neil Hall Water and other drinks are laid out near a tower block severely damaged by a serious fire, in north Kensington, West London, Britain June 14, 2017. REUTERS/Neil Hall Flames leap from a tower block severly damaged by a serious fire, in north Kensington, West London, Britain June 14, 2017. REUTERS/Neil Hall A man comforts a boy after a tower block was severly damaged by a serious fire, in north Kensington, West London, Britain June 14, 2017. REUTERS/Neil Hall Firefighters stand amid debris in a childrens playground near a tower block severly damaged by a serious fire, in north Kensington, West London, Britain June 14, 2017. REUTERS/Neil Hall Up Next See Gallery Discover More Like This HIDE CAPTION SHOW CAPTION of SEE ALL BACK TO SLIDE

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 it 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."

Grenfell Tower has around 130 units. It is located about a mile northwest of Kensington Palace and is also near the Portobello Road market tourist attraction.

One dazed-looking man wearing a green bathrobe told reporters that he had "lost my wife on the staircase."

He added: "I don't know what happened to her. I'm trying to find out where she is."

James Wood, 32, who lives nearby, told NBC News he watched children "at the window screaming for help ... and the room eventually went up in flames."

Sajad Jamalvatan, a Grenfell Tower resident who was at the movies when the fire broke out, told NBC News that he "saw with my bare eyes someone jumping from the building."

The London Fire Brigade sent 40 vehicles to the scene after being called at 12:54 a.m. Wednesday local time (7:54 p.m. ET Tuesday). At least 20 patients were in critical condition, officials said.

By noon local time (7 a.m. ET), flames were still visible from some of the apartment block's windows.

Surrounding streets up to a mile away were covered in a layer of ash as a police helicopter buzzed over the area — an ethnically and economically diverse part of west London.

Ousama Itani, who lives nearby, told NBC News that one of his relatives heard people screaming from the building.

"We saw apartment after apartment getting lit up into flames," Itani added.

Nassima Boutrig, who lives opposite the tower, told the Associated Press that she heard people shouting: "Help, help, help."

She added: "The fire brigade could only help downstairs. It was fire up, up, up. They couldn't stop the fire."

Residents were hurrying along the streets trying to find news of neighbors or family members.

Kidan Opbekke, 39, was returning to her home in a nearby street after working a night shift when she saw the aftermath of the blaze.

"A friend of mine, from Eritrea, she cannot find her daughter," she sobbed in the street. "She got out from the fire but she cannot find her daughter."

Opbekke added: "This is terrible. There is nothing we can do except pray. We just came here to pray. And why, why did this happen?"

At the nearby Latymer Community Church, some of the shocked survivors were being given water and food. A local mosque also opened its doors.

"We will be providing temporary shelter and food for anyone of any faith or no faith affected by the fire," said Abdurahman Sayed, the head of the Al Manaar Mosque.

Authorities said the cause of the blaze remained unclear. Forensic investigators with cameras and protective suits were visible at the scene.

A structural engineer was sent to the scene to monitor whether the high-rise remained stable.

A newsletter distributed by Grenfell Tower's managers in May 2016 advised that "you are generally safest to stay put in your home to begin with; the fire brigade will arrive very quickly if a fire is reported."

It added that "smoke detection systems have been upgraded and extended" as part of a $12.8 million refurbishment project.

However, residents complained about fire safety standards in November — warning that only a serious blaze would make authorities listen.

Rydon, the firm which carried out the refurbishment, released a statement Wednesday saying its work "met all required building control, fire regulation and health and safety standards."

Alastair Jamieson, Chloe Hubbard, Mo Abbas, Will Clark, Emma Ong, Nick Bailey, F. Brinley Bruton, Rachel Elbaum, Sophie Harris, Tony Hemmings and Jason Cumming reported from London. Alex Johnson reported from Los Angeles. Erin Dean, E.D. Cauchi and Rima Abdelkader reported from New York. The Associated Press contributed to this report.

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