A huge fire still burning in a Hong Kong apartment complex that has killed at least 44 people and left almost 300 missing may have been spread by unsafe scaffolding and foam materials used during maintenance work, police said on Thursday.

Working through the night, firefighters were struggling to reach residents potentially trapped on the upper floors of the Wang Fuk Court housing complex due to the intense heat and thick smoke from the fire that erupted on Wednesday afternoon. The complex in the northern Tai Po district has 2,000 apartments in eight blocks.

By early Thursday morning, authorities said they had brought the fire four in blocks under control, with operations continuing in three blocks after more than 15 hours.

Video from the scene showed flames still leaping from at least two of the 32-storey towers and heavy smoke billowing from several.

Police said in addition to the buildings being covered with protective mesh sheets and plastic that may not meet fire standards, they discovered some windows on one unaffected building were sealed with a foam material, installed by a construction company carrying out maintenance work.

“We have reason to believe that the company’s responsible parties were grossly negligent, which led to this accident and caused the fire to spread uncontrollably, resulting in major casualties,” Eileen Chung, a Hong Kong police superintendent, said.

Three men from the construction company, two directors and one engineering consultant, had been arrested on suspicion of manslaughter over the fire, she added.

The green construction mesh and bamboo scaffolding used on the buildings are a mainstay of traditional Chinese architecture but have been subject to a phase-out in Hong Kong since March for safety reasons.

A firefighter was among the 44 killed, with 45 people in hospital in critical condition, Hong Kong police told a press conference before dawn on Thursday.

The death toll is now the highest in a Hong Kong fire since World War Two, surpassing the 41 killed in a blaze in a commercial building in the Kowloon district in November 1996.

The latest fire has prompted comparisons to the Grenfell Tower inferno that killed 72 people in London in 2017. That fire was blamed on firms fitting the exterior with flammable cladding, as well as failings by the government and the construction industry.

“The priority is to extinguish the fire and rescue the residents who are trapped,” Hong Kong leader John Lee told reporters earlier. “The second is to support the injured. The third is to support and recover. Then, we’ll launch a thorough investigation.”

Some 279 people were uncontactable and 900 were in eight shelters, he added.

One 71-year-old resident surnamed Wong broke down in tears, saying his wife was trapped inside.

Harry Cheung, 66, who has lived at Block Two in one of the complexes for more than 40 years, said he heard a loud noise about 2:45 p.m. (0645 GMT) and saw fire erupt in a nearby block.

“I immediately went back to pack up my things,” he said.

“I don’t even know how I feel right now. I’m just thinking about where I’m going to sleep tonight.”

The Philippine foreign ministry said in a statement that its consulate in Hong Kong had received unverified information that some Filipino domestic workers may be trapped inside the buildings. It said it was coordinating with the police to assist any Filipino national affected.

China’s Xi urges ‘all-out’ effort against fire

On Wednesday, frames of scaffolding were seen tumbling to the ground as firefighters battled the blaze, while scores of fire engines and ambulances lined the road below the development.

From the mainland, China’s President Xi Jinping urged an “all-out effort” to extinguish the fire and to minimise casualties and losses, China’s state broadcaster CCTV said.

Hong Kong’s sky-high property prices have long been a trigger for social discontent in the city and the fire tragedy could further stoke resentment towards authorities ahead of a city-wide legislative election in early December.

Hong Kong’s Transport Department said that a number of roads would remain closed in the area on Thursday morning and 39 bus routes have been diverted.

At least six schools will be closed on Thursday due to the fire and traffic congestion, the city’s Education Bureau said.

A public inquiry yielded sweeping updates to building standards and fire safety regulations in high-rise offices, shops and homes.

Bamboo scaffolding being phased out

Hong Kong is one of the last places in the world where bamboo is still widely used for scaffolding in construction.

On mainland China, where use of bamboo in construction originated from ancient times, scaffolding is now mainly metal.

Hong Kong’s government moved to start phasing out bamboo scaffolding in March, citing worker safety after 22 deaths involving bamboo scaffolders between 2019 and 2024. It announced that 50% of public construction works would be required to use metal frames instead.

Though fire hazard was not cited as a reason for the phase-out, there have been at least three fires involving bamboo scaffolding this year, according to the Association for the Rights of Industrial Accident Victims in Hong Kong.

Wang Fuk Court is one of many high-rise housing complexes in Hong Kong, one of the most densely populated areas in the world. Tai Po, located near the border with mainland China, is an established suburban district with some 300,000 residents.

Occupied since 1983, the complex is under the government’s subsidised home ownership scheme, according to property agency websites. According to online posts, it has been undergoing renovations for a year at a cost of HK$330 million ($42.43 million), with each unit paying between HK$160,000 and HK$180,000.

Owning a home is a distant dream for many in Hong Kong, one of the world’s most expensive housing markets and where residential rents are hovering around record highs.