Samira Lamrani said she saw a woman drop a baby from a window on the ninth or 10th floor to people on the sidewalk.
People leave donations near the burning 24 storey residential Grenfell Tower block in Latimer Road, West London. "As I was going down the stairs, there were firefighters, truly unbelievable firefighters that were actually going upstairs, to the fire, trying to get as many people out the building as possible", he told the BBC.
Policing and fire minister Nick Hurd said checks are now planned on similar tower blocks. Twelve were confirmed to have died and more than 70 treated in hospital.
The trigger for the fire has been attributed to a faulty fridge on one of the lower floors - the third or fourth floor - however some eyewitnesses also reported seeing blue flames which could indicate a gas explosion.
Construction firm Rydon, which carried out a £8.6m refurbishment of the exterior of Grenfell Tower previous year, installing cladding and new windows, said its work "met all required building control, fire regulation, and health and safety standards".
In a blog post in November, it accused the Kensington and Chelsea Tenants' Management Organization (KCTMO), which manages the housing block on behalf of the local authority, of allowing "dangerous living conditions and neglect of health and safety legislation".
Grenfell Tower was fitted with zinc rain-screen cladding and glazed curtain walling after the 10-million-pounds refurbishment previous year.
"In my 29 years of being a firefighter, I have never, ever seen anything of this scale", Fire Commissioner Dany Cotton said.
Witnesses said they heard screaming from the upper floors as the flames raced up the tower.
"I saw people jumping out of their windows", Khadejah Miller, who was evacuated from her home nearby, told AFP.
But the building was already engulfed in fire, according to Joe Ruane, the former deputy chief fire officer for U.S. Air Force bases in Britain.
"When something like this happens sometimes you do feel a bit helpless but at the same time we know that some people have lost everything". But the smoke covered them.
In this photo taken from aerial video, smoke rises from a high-rise apartment building on fire in London, June 14, 2017.
Nassima Boutrig, who lives across from the building, said she was awakened by sirens and smoke so thick that it filled her home as well.
Paul Fuller, chairman of the Fire Sector Federation, said sprinklers could have helped lessen the impact of the fire.
Nigel went on: "200 firefighters were there tackling the blaze and many of whom actually going into the building".
"There was a huge outpouring from the community to say "we want to do something".
"This is mass murder and these people need to be put into court", he said. "I could not find the stairs". It said the cause of the blaze would be "fully investigated".
The tower was built in 1974. According to minutes of a KCTMO board meeting in July 2016 said works were carried out to address the issues raised in the enforcement notices. "They have very complex and effective fire protections and life-safety systems that all work together to get fires out quickly and absolutely confine them to the suite of origin".