It is believed that several hundred people were inside Grenfell Tower when it was engulfed in flames.
Witnesses have told how they were woken by screaming in the early hours after a fire hit 27-storey building in north Kensington.
One local resident, called Tamara, has described how desperate parents trapped inside the building were resorting to throwing their children out of the windows to avoid the horrific fire.
‘Around 12.30/1am my mum called me and said there was a fire outside. By the time I got there the whole right side of the building was on fire, the whole thing was engulfed in flames.
‘We could hear people screaming ‘Help me’ so me and my brother, with some other people who live in the area, ran over to the estate to where you could still get underneath it and there were people just throwing their kids out saying “Save my children”.
‘The fire crew, ambulance and police couldn’t do anything, they couldn’t get in, and they were just telling them to stay where they are, and we’ll come and get you,’ she told HBBC. ‘But things quickly escalated beyond measure and they couldn’t go back in and get them.
‘Within another 15 minutes the whole thing was up in flames and there were still people at their windows shouting ‘Help me’. You could see the fire going into their houses and engulfing the last room that they were in.’
Other onlookers in west London have described the terrifying scenes and have told of the bravery of the emergency services, who continue to battle the huge blaze to save those trapped inside.
Jody Martin said he got to the scene just as the first fire engine was arriving at Grenfell Tower, in Latimer Road.
‘I grabbed an axe from the fire truck, it looked like there was a bit of confusion about what to do.
‘I ran around the building looking for a fire escape and couldn’t see any noticeable fire escapes around the building. A lot of debris falling down.
‘I eventually gained entry on to the second floor, and once I got to the corridor I realised there was so much smoke there.’
He said that the smoke pouring from the building was so thick, he would be surprised if anyone could have left the building without assistance.
‘I watched one person falling out, I watched another woman holding her baby out the window… hearing screams,
I was yelling everyone to get down and they were saying “We can’t leave our apartments, the smoke is too bad on the corridors”,’ he said.
Fabio Bebber wrote on Twitter: ‘More screams for help as the fire spreads to another side of the building.
‘We can see how quick the fire spreads via the external panels. It’s unbearable hearing someone screaming for their lives at #grenfelltower.#
George Clarke, who presents the Channel 4 TV show Amazing Spaces, told Radio 5 Live: I was in bed and heard ‘beep, beep, beep’ and thought, ‘I’ll get up and run downstairs as quickly as I could’.
‘I thought it might be a car alarm outside and saw the glow through the windows.
‘I’m getting covered in ash, that’s how bad it is. I’m 100 metres away and I’m absolutely covered in ash.
‘It’s so heartbreaking, I’ve seen someone flashing their torches at the top level and they obviously can’t get out.
‘The guys are doing an incredible job to try and get people out that building, but it’s truly awful.’
A man called Michael, who lives on the seventh floor of the tower block, told Sky News how he rescued a girl after the blaze took hold.
London Fire Brigade assistant commissioner Dan Daly said: ‘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 Ambulance said it had sent a “number of resources” to the scene, including its Hazardous Area Response Team.
London mayor Sadiq Khan tweeted: ‘Major incident declared at Grenfell Tower in Kensington’ and urged people to follow London Fire Brigade on Twitter.
Fire crews from north Kensington, Kensington, Hammersmith and Paddington and surrounding stations were at the scene with the fire burning from the second to the top floor.
The cause of the fire was not known at this stage, London Fire Brigade said.