What we know about the Hong Kong apartment fires

A devastating fire has ripped through a high-rise public housing complex in Hong Kong, killing at least 55 people, making it the city's deadliest in more than 60 years. More than 270 people have been reported missing and thousands of residents are in evacuation shelters.

Images from the scene show several of the high-rise blocks still ablaze, and thick smoke billowing into the air, dominating the Chinese territory's skyline.

Three men have been arrested on suspicion of manslaughter connected to the fire, according to local media reports, and an investigation has been launched.

Chinese President Xi Jinping has expressed condolences to victims, including a "firefighter who died in the line of duty", state media report.

What caused the blaze is still unclear, but here is what we do know, so far.

The cause of the fire is unknown but a preliminary investigation found that the rapid speed at which it spread was unusual, Hong Kong's security secretary said early on Thursday morning.

Police say a mesh material and plastic sheets were found on the outside of the buildings - both of which are not believed to be fireproof.

Styrofoam was also found on the building's windows - and that, together with the other construction materials is likely to have caused the flames to spread so quickly, said police.

Police have arrested three men aged between 52 and 68 on suspicion of manslaughter in connection with the deadly blaze - two of them are directors of a construction firm while the other is an engineering consultant.

A police spokesperson said investigators were looking into the alleged actions, or failure to act, of the firm's top officials.

"We have reason to believe that those in charge at the company were grossly negligent, which led to this accident and caused the fire to spread uncontrollably, resulting in major casualties," said the spokesperson.

Local media reports also quote some residents who say the fire alarms in the building did not go off.

This is Hong Kong's deadliest fire in at least 63 years and has been classified as a level five alarm - the highest in severity.

Within 40 minutes of first being reported, it was declared a level four, but by 18:22, about three and a half hours later, the level was raised again.

Local media had earlier reported that explosions could be heard inside the building and fire hoses could not easily reach the higher levels.

The ferocity of the heat had prevented firefighters from entering the buildings to conduct rescue operations, deputy director of fire services Derek Armstrong Chan told media.

As well as 767 firefighters, 128 fire engines, 57 ambulances and some 400 police officers were deployed.

Among the dead is firefighter Ho Wai-ho, 37, who was with the service at Sha Tin Fire Station for nine years.

The fire service says it lost contact with him at 15:30, and about half an hour later, found that he had collapsed. He was taken to hospital but declared dead shortly after.

"I am profoundly grieved at the loss of this dedicated and gallant fireman," said Andy Yeung, director of the fire service.

At least one other firefighter is in hospital, the Hong Kong fire service said.

Police officers have been helping residents search for family members by using a loudspeaker, say local media reports.

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