The fire that engulfed the 24-storey Grenfell Tower block of apartments in the north Kensington area killed at least 12 people and injured 78 others in an inferno that trapped residents as they slept.

More than 200 firefighters, backed up by 40 fire engines, fought for hours to try to bring the blaze, one of the biggest seen in central London in memory, under control.

Police Commander Stuart Cundy said a “recovery operation” could take some time and there could be people in the building who are unaccounted for, though he would not be drawn on a figure.

Firefighting crews still had to reach the top four floors of the building where several hundred people live in 120 apartments.

The cause of the inferno, which left the tower block a charred, smoking shell, was not immediately known.

London mayor Sadiq Khan said the fire raised questions over safety of high-rise blocks like Grenfell Tower.

Campaigners for residents of the London tower block spoke angrily about long-standing fire safety concerns, saying they were ignored because the community was not rich.

Damian Collins, former head of the Grenfell Tower Residents’ Association, said residents had complained to the local council over the handling of a major refurbishment of the building completed last year.

“We used to say that... it’ll take a tragedy before the people wake up and before the people managing the building get held to account,” Collins said.

Collins said residents of the tower were particularly concerned about the lack of fire exits in the building.

He said there were also faults in the heating and lighting systems, and 90 per cent of residents had signed a petition in 2015 that was ignored.

“There were so many concerns,” Collins said.

Aside from the building’s allegedly flawed warning mechanisms, there appears to have been no central sprinkler system in the recently renovated apartment building, according to residents who spoke to London’s Evening Standard newspaper. It remained unclear whether the building lacked sprinklers entirely, or whether they failed.

Standing near the burned-down apartment building, residents also reproached authorities , saying that members of a fire brigade had checked alarms in the building as recently as Saturday. Residents said that during those visits, officials advised them to stay inside their apartments in case of a fire emergency.

“They told us the protocol is to close your door, because the fire door will withstand the heat for a duration of time. But I think what’s happened is they’re not understanding that this fire has spread all around the building,” said one resident. Other residents said they were told that their units were fireproof for at least an hour.

Grenfell Tower, a 24-storey apartment block in North Kensington, West London, was completed in 1974.

It is managed by Kensington and Chelsea Tenant Management Organisation (KCTMO) on behalf of Kensington and Chelsea London Borough Council.

Watch: massive blaze at London apartment bock

A 8.7 million pound (US$11 million) refurbishment of the block was carried out by construction company Rydon and completed in July 2016. It included new external cladding, replacement windows and curtain wall facades.

Rydon said its refurbishment of the building met all required building control, fire regulation and health & safety standards.

The local council said it was focusing on supporting the rescue and relief operation. It said the causes of the fire would be fully investigated.

The Washington Post, Agence France-Presse, Reuters