Hong Kong’s worst fire in decades was still smoldering in several apartment towers Thursday as firefighters struggled to rescue dozens of people still unaccounted for.

At least 55 people were known to have died in the blaze that broke out Wednesday at Wang Fuk Court in Taipo, a suburb in the city's mountainous New Territories. Dozens more were injured, and about 900 of the 4,800 residents were evacuated to temporary shelters overnight.

Seven of the 32-story towers in the eight building complex were engulfed in flames after construction materials and bamboo scaffolding caught fire. Officials said that extreme heat was hampering rescue efforts.

It's the deadliest fire in Hong Kong since November 1996, when 41 people died in a commercial building in Kowloon in a fire that lasted for around 20 hours.

Here's what to know about the disaster:

Why the buildings burst into flames

Officials are investigating why construction materials, netting and bamboo scaffolding being used in renovations to the outsides of the high-rise buildings at Wang Fuk Court caught fire.

In the meantime, authorities arrested three people, the directors and an engineering consultant of a construction company, on suspicion of manslaughter. Police did not name the company, but they searched the office of Prestige Construction & Engineering Co., which The Associated Press confirmed was in charge of the renovations. Phone calls to the company's offices went unanswered.

Officials said they suspect that some materials, such as plastic foam panels being used to protect windows from damage, did not meet fire resistance standards. High winds helped spread the flames.

The type of buildings affected

About a third of Hong Kong residents live in the government's Housing Authority dwellings. Wang Fuk Court is a complex of privately-owned, but subsidized housing.

Built in the 1980s, the very basic apartments measure 40-45 square meters (430-485 square feet), according to online real estate listings. Like most Hong Kong mass market housing, they appear not to be equipped with smoke detectors or sprinkler systems.

The buildings were constructed before revisions to Hong Kong's fire codes required mandatory fire refuge floors. Seven of the eight towers in Wang Fuk Court caught fire.

Hong Kong's 7.5 million residents mostly live in cramped apartments crammed on scarce flat lands or perched on the slopes of steep mountainsides. Many of those high-rise buildings are crowded closely together.

How Hong Kong's authorities have responded

Firefighters struggled to bring the blazes under control as their ladders and hoses could only reach just over halfway up the 32-story buildings, or about 53 meters (174 feet) — under 20 stories.

High winds and extremely high heat may have prevented use of aerial equipment such as helicopters. The high temperatures also deterred firefighters from entering the buildings to fight the blaze and rescue survivors, said Derek Armstrong Chan, deputy director of Hong Kong's Fire Service Operations.

Hong Kong Chief Executive John Lee said the government would set up a task force to conduct a full investigation into the disaster. He said the case would be submitted to the Coroner’s Court, which conducts inquiries into the causes and circumstances of certain deaths.

Lee said the government planned to inspect all housing estates undergoing major repairs to review the safety of scaffolding and construction materials. He also promised to provide “all possible support” to those affected by the fire.

Helping the survivors

The hundreds of survivors who were evacuated or were outside the buildings at the time the fire started were staying in temporary shelters, including a nearby school.

There, workers were distributing bottled water, food and other necessities. Volunteers were bringing supplies like water and snacks.

Reports cited Hong Kong's Hospital Authority as saying that as of early Thursday, of the 62 people sent to hospitals for treatment, 17 were in critical condition.