Police say the cause of a huge blaze in a Hong Kong apartment complex that killed at least 83 people – with about 300 still missing – could have been “grossly negligent” builders using unsafe materials.

By Friday morning (AEDT), firefighters had mostly doused the blaze that tore through the Wang Fuk Court housing complex in the northern district of Tai Po.

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 complex.

Firefighters battled the massive blaze at Wang Fuk Court throughout the night. Photo: AAP

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

Video showed firefighters with torches searching through the charred remains of the towers on Thursday night.

A distraught woman carrying her daughter’s graduation photograph searched for her child outside a shelter, one of eight that authorities said were housing 900 residents.

“She and her father are still not out yet,” said the 52-year-old, who gave only her surname, Ng, as she sobbed.

“They didn’t have water to save our building.”

On Thursday, police officers searched the building maintenance company responsible for the housing estate, which had been under renovation. They seizing documents, computers and phones.

“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.

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.

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

Police arrested two directors and an engineering consultant of Prestige Construction, a business contracted to do the maintenance.

Police said those arrested were under suspicion of manslaughter for using unsafe materials.

Prestige did not answer repeated calls for comment.

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

Residents at a temporary shelter near the fire scene. Photo: AAP

The confirmed death toll rose to 83 as of midnight in Hong Kong on Thursday, The South China Morning Post reported, citing the fire department.

That made it Hong Kong’s deadliest fire since 1948, when 176 people were killed in a warehouse blaze.

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

Two Indonesian migrant workers “in the domestic sector” died in the fire and two others were injured, the South-East Asian nation’s foreign ministry said.

“The priority is to extinguish the fire and rescue the residents who are trapped,” city leader John Lee said, adding that support for the injured and recovery efforts would follow, and then a thorough investigation.

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

“Our hearts go out to all those affected by the horrific fire in Hong Kong,” the Grenfell United survivors’ group said on social media.

“To the families, friends and communities, we stand with you. You are not alone.”

Many residents took to social media to criticise what they saw as negligence and cost-cutting as a cause of the fire.

One video showed construction workers smoking on the bamboo scaffolding surrounding one block of the complex during renovation.

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

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

Occupied since 1983, the complex is under the government’s subsidised home ownership scheme, according to property agency websites.

Lee said the government would set up a HK$300 million ($60 million) fund to help residents.

Chinese companies and groups, including car makers Xiaomi, Xpeng and Geely, as well as the charity foundation of Alibaba’s founder Jack Ma and Tencent, announced donations.

“We bought in this building more than 20 years ago,” said a 51-year-old resident surnamed Wan.

“All of our belongings were in this building, and now that it has all burned like this, what’s left?”

An online app showed reports of missing persons submitted through a linked Google document that detailed residents of individual towers and rooms. It includes descriptions such as “Mother-in-law in her 70s, missing” or “one boy and one girl” or “Rooftop: 33-year-old male.”

One simply reads “27th floor, room 1: He is dead.”

Reuters could not independently verify the information on the app.

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

-with AAP