A deadly overnight fire raced through a 24-story apartment tower in London on Wednesday, killing at least six people and injuring 74 others. One desperate woman threw a baby out of a high window and a man on the ground managed to catch the child, a witness said.

Flames from the inferno lit up the night and black smoke spewed from the windows of the Grenfell Tower in North Kensington where more than 200 firefighters battled the blaze. A plume of smoke stretched for miles (kilometres) across the sky after dawn, revealing the blackened, flame-licked wreckage of the building, which was still burning over 12 hours later.

鈥淭his is an unprecedented incident,鈥� Fire Commissioner Dany Cotton told reporters. 鈥淚n my 29 years of being a firefighter I have never, ever seen anything of this scale.鈥�

She told reporters she feared firefighters would find more victims still inside the building.

Crews are still working tirelessly to extinguish the fire & are systematically searching the building

鈥� London Fire Brigade (@LondonFire)

People in apartments enveloped by the quickly advancing flames and thick smoke banged on windows and screamed for help to those watching down below, witnesses and survivors said. One resident said the fire alarm did not go off.

Police commander Stuart Cundy gave the death toll but added the figure was likely to rise 鈥渄uring what will be a complex recovery operation over a number of days.鈥�

Paul Woodrow, head of operations for the London Ambulance Service, said 20 of the injured were in critical condition.

The London Fire Brigade received the first reports of the fire at 12:54 a.m. and the first engines arrived within six minutes, Cotton said.

There was no immediate word on the cause of the blaze, but angry residents said they had warned local authorities about fire issues at Grenfell Tower. The public housing block of 120 apartments was built in 1974 and recently upgraded at a cost of 8.6 million pounds ($11 million), with work finishing in May 2016, according to the Royal Borough of Kensington and Chelsea.

Samira Lamrani, a witness, said a woman dropped a baby from a window on the ninth or 10th floor to people on the sidewalk.

鈥淧eople were starting to appear at the windows, frantically banging and screaming,鈥� Lamrani said, adding the woman gestured that she wanted to drop a baby.

鈥淎 gentleman ran forward and managed to grab the baby,鈥� Lamrani told Britain鈥檚 Press Association news agency.

鈥淭he flames, I have never seen anything like it, it just reminded me of 9-11,鈥� said Muna Ali, 45. 鈥淭he fire started on the upper floors 鈥� oh my goodness, it spread so quickly. It had completely spread within half an hour.鈥�

Other witnesses described a white, polystyrene-type material falling like snow from the building as it burned. Some feared the charred tower block might collapse but a structural engineer said the building was not in danger, London Fire Brigade said, adding 鈥渋t is safe for our crews to be in there.鈥�

Ruks Mamudu, 69, escaped from her first floor apartment wearing only her purple pyjamas and bathrobe. She and her grandson sat outside the building and watched people trapped on higher floors cry desperately for help.

鈥淚 sat there watching my house burn down and watching people cry for help who couldn鈥檛 come down,鈥� she said.

People at the scene spoke of being unable to reach friends and family inside. Others said they could see people inside using flashlights and mobile phones to try to signal for help from higher floors.

Nassima Boutrig, who lives opposite the building, said she was awakened by sirens and smoke so thick that it filled her home as well.

鈥淲e saw the people screaming,鈥� she said. 鈥淎 lot of people said 鈥楬elp! Help! Help!鈥� The fire brigade could only help downstairs. It was fire up, up, up. They couldn鈥檛 stop the fire.鈥�

The disaster occurred 10 days after a terror attack at London鈥檚 Borough Market. Some residents initially feared the fire was also terror-related, though authorities discounted that possibility.

Edward Daffarn, a 55-year-old who lived on the building鈥檚 16th floor, said the fire alarm didn鈥檛 ring. Daffarn said residents had complained for years to London City Council about building safety, to no avail.

鈥淚鈥檓 lucky to be alive. A neighbour鈥檚 smoke alarm went off and another neighbour phoned and told me to get out,鈥� he said. 鈥淚 consider this mass murder.鈥�

The Grenfell Action Group, a community organization formed to oppose a nearby redevelopment project, has been warning about the risk of fire at Grenfell Tower since 2013. The group has raised concerns about testing and maintenance of firefighting equipment and blocked emergency access to the site.

鈥淎ll our warnings fell on deaf ears and we predicted that a catastrophe like this was inevitable and just a matter of time,鈥� the group said in a blog after the fire broke out.

A July 2014 newsletter for residents said the building was designed 鈥渁ccording to rigorous fire safety standards鈥� and recommended that in case of a fire residents should stay inside their apartments.

The British company that carried out the tower鈥檚 2016 refurbishment, Rydon, said in a statement its work 鈥渕et all required building control, fire regulation, and health and safety standards.鈥�

London Mayor Sadiq Khan said many questions now need to be answered about tower blocks around the city.

鈥淭here will be a great many questions over the coming days as to the cause of this tragedy and I want to reassure Londoners that we will get all the answers,鈥� Khan said.

Prime Minister Theresa May鈥檚 Downing Street office said she was 鈥渄eeply saddened by the tragic loss of life in the Grenfell Tower and is being kept constantly updated on the situation.鈥�