'Negligent' builders blamed for HK blaze that killed 55

Hong Kong firefighters have brought under control a huge blaze in an apartment complex that killed at least 55 and left nearly 300 missing, while police say its cause could have been a "grossly negligent" construction firm using unsafe materials.

Rescuers battled intense heat and thick smoke for more than a day after the blaze erupted as they fought to reach residents feared trapped on the upper floors of the Wang Fuk Court housing complex in the northern district of Tai Po.

Responding to Hong Kong's deadliest fire in 77 years, its leader John Lee said the government would set up a $HK300 million ($A59 million) fund to help residents.

The city's development bureau had also discussed gradually replacing bamboo scaffolding across the Asian financial hub with metal scaffolding as a safety measure.

The eight blocks of the tightly packed complex have 2000 apartments home to more than 4600 people in the financial hub struggling to overcome chronic shortages of affordable housing.

On Thursday, police officers searched the building maintenance company responsible for the housing estate, seizing documents that mentioned it, media said.

The government identified the registered contractor for the complex as Prestige Construction and Engineering Company Limited.

Prestige did not answer repeated calls for comment.

Police seized bidding documents, a list of employees, 14 computers and three mobile phones during Thursday's raid of the Prestige office, the government said.

"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," police superintendent Eileen Chung said.

Chinese President Xi Jinping urged an "all-out effort" to extinguish the fire and minimise casualties and losses, state broadcaster CCTV said.

The fire poses a challenging test for Beijing's grip on the city it has transformed since the mass pro-democracy protests of 2019.

Video images from the scene showed flames leaping from at least two of the 32-storey towers sheathed in green construction mesh and bamboo scaffolding.

Authorities said they had doused the flames in four of seven affected blocks, with those in the rest brought under control.

Police said that as well as the protective mesh and plastic coverings of the buildings, which might fall short of fire standards, they found foam material sealing some windows on one unaffected building, and installed by a construction company engaged in year-long maintenance work.

Police have arrested two directors and an engineering consultant of the company on suspicion of manslaughter over the fire, Chung said.

The estate had been under renovation for a year, media said.

Hong Kong's corruption body said it had launched an investigation into suspected graft related to the renovation.

A firefighter was among the dead, while dozens in hospital were in critical condition, authorities said.

About 279 people have yet to be traced.

More than 1200 firefighters are battling to control the flames, along with 304 fire engines and rescue vehicles.

The fire has prompted comparisons to London's Grenfell Tower inferno that killed 72 people 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.

Chinese companies and groups that have announced donations to the fire victims include auto makers Xiaomi, Xpeng and Geely, as well as the charity foundation of Alibaba's founder Jack Ma.

Wang Fuk Court is one of many high-rise housing complexes in Hong Kong, one of the world's most densely populated cities.

Tai Po, near the border with mainland China, is an established suburban district home to about 300,000.

Occupied since 1983, the complex is under the government's subsidised home ownership scheme, according to property agency websites, a lifeline for the city's middle-income families.