At least six people have died after a huge fire destroyed a tower block in west London, with the death toll expected to rise.
Flames tore up the 24-storey Grenfell Tower in north Kensington, leaving people trapped on upper floors, some holding babies from windows and others jumping from their flats.
Commander Stuart Cundy, of the Metropolitan Police, said: "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."
Fire crews are searching the tower and Mr Cundy added: "I do anticipate that there may be people within that building that are as yet unaccounted for."
NHS England said 74 people are being treated in six hospitals across the capital, of whom 20 are in critical care.
Mr Cundy said it is likely to be some time before police can identify the victims, adding that it is too early to speculate on the cause of the fire.
Prime Minister Theresa May was said to be "deeply saddened by the tragic loss of life" and newly appointed police and fire minister Nick Hurd will chair a meeting of the Civil Contingencies Secretariat to co-ordinate the response.
London Fire Commissioner Dany Cotton told reporters: "This is an unprecedented incident. In my 29 years of being a firefighter, I have never ever seen anything of this scale."
Grenfell Tower was built in 1974 and contains 120 flats thought to be home to between 400 and 600 people.
The building was refurbished recently at a cost of £8.6 million, with work completed in May last year.
Rydon, the firm that carried it out, said its work "met all required building control, fire regulation, and health and safety standards".
London Fire Brigade said the cause of the fire is still being investigated, but several residents reported one man had said it started in his faulty fridge.
The brigade said a structural engineer had checked the building and determined it was not in danger of collapse and that rescue teams were safe to be inside.
Many traumatic accounts of the fire and its impact have emerged, including a baby being dropped from the tower.
Samira Lamrani said she saw a woman try to save the baby by dropping it from a window ''on the ninth or 10th floor'' to waiting members of the public below.
Residents who escaped complained there had been no fire alarm, with many relying on neighbours to wake them as the blaze spread.
They said official advice in the event of a fire had been to stay inside.
Michael Paramasivan, who was in his seventh floor flat with girlfriend Hannah West, 23, and her daughter Thea, five, said: "If we'd listened to them and stayed in the flat we'd have perished."
A residents' action group said its warnings about safety had fallen on "deaf ears".
A blog post from Grenfell Action Group in November said "only a catastrophic event" would expose the concerns residents had.
The group said there was one entry and exit to the tower during improvement works and it had issues with evacuation procedures.
London mayor Sadiq Khan said: "There 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."
Witnesses said the fire spread rapidly up the building, with some suggesting it was fuelled by gas.
Mr Paramasivan, 37, told the Press Association: "There were explosions everywhere you looked, lots of bangs, blue gas coming out everywhere you looked.
"About 12 floors up I saw three children waving from a window and then there was just an explosion and they disappeared.
"They were three kids, they were banging on the windows, you could see their silhouettes and then bang, it just went up."
Muna Ali, 45, said: "The flames, I have never seen anything like it, it just reminded me of 9/11.
"The fire started on the upper floors ... oh my goodness, it spread so quickly, it had completely spread within half an hour."
Robert Black, chief executive of Kensington & Chelsea Tenant Management Organisation, which manages Grenfell, said: "The fire at Grenfell Tower is devastating and the reports of injury and losses of life absolutely heartbreaking."
Tiago Etienne, 17, said: "I just heard people screaming 'help, help', and I saw the entire estate was in flames.
"I saw children being thrown out of the building from as high as about the 15th floor. They were young - aged probably between four and eight. I saw three thrown out.
"I think they were being thrown out for the firefighters or police to catch, but I couldn't see from where I was who was at the bottom and what they were catching them in."
Several firefighters were injured as they tackled the blaze, Ms Cotton said.
The fire chief added that a "major investigation" would take place once the search and rescue operation had concluded
"Unfortunately, a number of firefighters have been injured but fortunately only with minor injuries, which, considering the scale and the number of my firefighters have been involved and how hard they have worked, is a testament to their professionalism and dedication," she said.
Asked if an inquiry would be carried out independent of the borough, Mr Khan said: "There are genuine concerns, reasonable concerns, that have been raised in the course of the night and it's really important that these questions are answered.
"I will be demanding answers and I can assure you I will be ensuring there is independence in relation to it.
"The reassurance we need is to make sure lessons are learned and also if - and this is a big if - if there are mistakes made, we want to make sure we learn from them."
Addressing concerns about potential design flaws existing in similar towers across London, he said: "There are tower blocks across London and across the country and they are the responsibility of the borough or a private management company and it's important people are reassured these towers are safe."
Flowers had been placed beside the taped-off police cordon, which was being guarded by uniformed officers.
Attached to a mixed bouquet was a card with the message: "Love and prayers to the families and victims. Justice has to be done. People before money. RIP."