London's Metropolitan Police say six people have died in the devastating fire that engulfed a west London apartment block. Police say the number is expected to rise.
Police commander Stuart Cundy says he 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."
Cundy says many others are receiving medical care.
London's Ambulance Service says 74 people are being treated following a massive apartment blaze in west London.
Paul Woodrow, the head of operations, says that 20 of those patients are in critical condition. He said that the patients were being treated for a range of injuries and smoke inhalation.
The London Fire Commissioner says several firefighters have sustained minor injuries in the fire at a west London apartment building, as fire crews continue searching the tower block for victims.
Dany Cotton told reporters Wednesday at midday that firefighters were still in the building, as authorities appealed for families to report anyone who was accounted for.
The scale of the inferno means it could be days before it is clear how many victims were claimed by the blaze.
Cotton said she did not want to speculate about the cause of the fire or how it spread so rapidly to engulf the whole tower block.
London Mayor Sadiq Khan says questions need to be answered about tower blocks around the city following a devastating fire.
Khan had been called to respond after reports that people had been advised in advance to remain in their flats in the event of fire.
Khan says in a statement "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."
Prime Minister Theresa May's office says the leader is "deeply saddened" by the devastating fire that engulfed a high-rise apartment block in west London.
May's office at Downing Street says in a statement that the leader is "deeply saddened by the tragic loss of life in the Grenfell Tower and is being kept constantly updated on the situation."
In Germany, a spokeswoman for Angela Merkel says the chancellor received the news "with great sadness."
Flames shot from windows all the way up the 24-story Grenfell Tower in North Kensington as more than 200 firefighters battled the blaze. A plume of smoke stretched for miles (kilometers) over the capital. The scent of acrid smoke hung in the air.
"This is an unprecedented incident," Fire Commissioner Dany Cotton told reporters on the scene. "In my 29 years of being a firefighter I have never, ever seen anything of this scale."
Local residents said they had warned local authorities about fire issues in the building, a public housing block built in 1974 and containing 120 homes, according to the Royal Borough of Kensington and Chelsea.
"We've complained to council," said Edward Daffarn, 55, who said nothing had been done to improve safety. "I consider this mass murder."
The construction firm that recently refurbished the west London tower that was engulfed in a deadly blaze says its work "met all required building control, fire regulation, and health and safety standards."
Rydon completed a 8.6 million-pound ($11-million) refurbishment project in 2016 on behalf of the local authority to modernize the exterior of Grenfell Tower, which saw new cladding and windows installed.
The company said it would not be commenting further "given the ongoing nature of the incident and the tragic events overnight".
The London Fire Brigade received the first reports of the fire at 12:54 a.m. and the first engines arrived within six minutes, she said.
The cause of the fire was not immediately known. Residents said the blaze appeared to start in an apartment on a lower floor and spread upward quickly.
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.
"We saw the people screaming," she said. "A lot of people said 'help, help, help.' The fire brigade could only help downstairs. It was fire up, up, up. They couldn't stop the fire."
Boutrig said her friend's brother, wife and children lived in the building and that her friend was waiting to find out if they were OK.
Other survivors spoke of confusion and conflicting advice given to residents, many of whom had been advised in advance not to leave their apartments in the event of a fire.
"There were no fire alarms," said Daffarn, who was warned by a neighbor to flee. "There was heavy smoke in the hallway. I could not find the stairs."
Others searched for information at makeshift evacuation centers set up at churches and recreation centers.
At St. Clement's Church, where evacuees gathered, Hadra Hassad was trying to find one of her closest friends, who lived on the 21st floor. Hassad says she believes one of her friend's daughters is in a hospital, but didn't know which one.
Several dozen dazed survivors gathered at the nearby Portobello Rugby Center. Some called friends and family to assure them they had survived. A variety of languages was heard.
National Health Service nurses and doctors clustered with groups of victims to see if emergency medicine or help was needed. Pastors provided counselling, while charity workers and local residents brought clothing, blankets, diapers and toys.
A local lawmaker appealed for clothes, blankets and toiletries for those who had left everything behind to save their lives.
Ambulances and fire trucks filled the streets around the building, which is located in a diverse, working class area of London. People who live nearby were evacuated, some carrying pets in their arms as they left. Volunteers handed out bottled water.
Helicopters hovered overhead. Exhausted firefighters sprawled on the pavement just inside the police cordon, drinking water from plastic bottles.
"Crews wearing breathing apparatus and extended duration breathing apparatus have been working in extremely challenging and difficult conditions to rescue people and bring this major fire under control," Cotton said.
George Clarke told Radio 5 Live that he was covered in ash even though he was 100 meters (yards) from the scene.
He said he saw people waving flashlights from the top levels of the building and saw rescuers "doing an incredible job" trying to get people out.
Grenfell Tower was recently upgraded at a cost of 8.6 million pounds ($11 million), with work finishing in May 2016.
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.
"All our warnings fell on deaf ears and we predicted that a catastrophe like this was inevitable and just a matter of time," the group said in a blog post written after the fire broke out.
Associated Press journalists Cara Rubinsky and Ben Jary contributed to this report.