Updated

Firefighters are battling a huge blaze at a west London high-rise block that houses more than 100 apartments. Here is what we know about the fire so far:

WHAT HAPPENED?

Reports of a fire at Grenfell Tower in North Kensington, west London, came in just before 1 a.m. on Wednesday.

The first fire crews arrived at the scene within minutes, and the London Fire Brigade soon declared it a major incident. The brigade sent 45 fire engines and over 200 firefighters to the scene.

Residents say the blaze appeared to start in an apartment on a lower floor and spread upward rapidly. The block was covered in thick black smoke and parts of it were still ablaze by midday Wednesday.

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WHAT'S THE DAMAGE?

Police confirmed Wednesday that 12 people died but they expect to toll to rise after a complex recovery operation that will last days.

Authorities say 65 people were rescued from the blaze. Ambulance officials say 78 people were being treated in hospitals across London for a range of injuries and smoke inhalation. Of those patients, 18 are in critical care.

Some witness reports say children and a baby were seen being thrown out of windows amid the blaze. It is not yet known how many people were in the building at the time and how many escaped.

The fire brigade says a structural engineer and expert crews believe the building is not in danger of collapsing.

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HOW DID IT START?

Authorities say the cause of the fire is not yet known and declined to speculate about how it started and spread so quickly.

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WHAT'S THE BUILDING LIKE?

Grenfell Tower is a 24-story public housing block containing 120 homes that is part of the Lancaster West Estate. It was built in 1974 and owned by the local authority, the Royal Borough of Kensington and Chelsea.

The building was recently upgraded at a cost of 8.6 million pounds ($11 million), with work to modernize the exterior finishing in May 2016.

But residents say the fire alarm didn't ring Wednesday, and that they had complained for years to local authorities about building safety in vain.

The Grenfell Action Group, a community organization, says it has repeatedly warned about the risk of fire at the building since 2013. The group has raised concerns about testing and maintenance of firefighting equipment and about blocked emergency access to the site in recent years.