by Holmes Chan and Tommy Wang

Hong Kong authorities said on Friday the death toll from the city's worst fire in decades had risen to at least 83, as firefighters scoured torched high-rise buildings for scores of people still listed as missing.

Flames were still visible in some of the eight-building apartment complex's almost 2,000 units well over 24 hours after the fire broke out, with crews still spraying water over the blackened exteriors.

Authorities have begun investigating what sparked the disastrous blaze -- the financial hub's worst in almost 80 years -- including the presence of bamboo scaffolding and plastic mesh wrapped around the structures as part of a housing estate-wide renovation.

Hong Kong's anti-corruption body said it has launched a probe into renovation work at the housing complex, hours after police said they had arrested three men on suspicion of negligently leaving foam packaging at the fire site.

Residents of Wang Fuk Court, located in Hong Kong's northern district of Tai Po, told AFP that they did not hear any fire alarms and had to go door-to-door to alert neighbours to the danger.

"The fire spread so quickly. I saw one hose trying to save several buildings, and I felt it was far too slow," said a man surnamed Suen.

"Ringing doorbells, knocking on doors, alerting the neighbours, telling them to leave -- that's what the situation was like," he said.

The intense flames were finally extinguished in four of the eight apartment blocks and the fires in three others were under control, officials said on Thursday afternoon. One building was not affected.

A "saddened" Pope Leo issued a statement sending "spiritual solidarity to all those suffering... especially the injured and the families who grieve".

- 'Cannot describe it' -

Of the 83 people confirmed dead by 12:00 am local time (1600 GMT Thursday), one was a 37-year-old firefighter and two were Indonesians working as migrant domestic workers.

It is Hong Kong's deadliest fire since 1948, when an explosion followed by a fire killed 135 people.

But the toll could yet rise further, with city leader John Lee saying in the early hours of Thursday that 279 people were unaccounted for.

Firefighters said later that they had made contact with some of those and authorities have not updated the figure since.

Police at a nearby community centre hoping to identify victims showed photos of bodies pulled from the fire to people seeking missing loved ones.

"If the faces are unrecognisable, there are personal items for people to identify," said a woman surnamed Cheung who was looking for her relatives.

"I cannot describe my feelings. There were children... I cannot describe it." 

A government spokesman told AFP on Thursday evening that of those being treated in hospital, 12 were in a critical condition, 29 were listed as serious and 17 were stable.

Deadly fires were once a regular scourge in densely populated Hong Kong, especially in poorer neighbourhoods, but improved safety measures have made them far less common.

Hong Kong authorities will immediately inspect all housing estates undergoing major works following the disaster, city leader Lee said. 

The city's number-two official Eric Chan told a news conference it was "imperative to expedite the full transition to metal scaffolding", adding that the government would collaborate with the construction industry. 

Chinese President Xi Jinping expressed condolences to the victims, according to state media, with the Hong Kong government saying Beijing would provide assistance such as drones and medicine. 

City authorities said they had opened nine shelters and were organising temporary accommodation and emergency funds for those who had lost their homes.

Activities around Hong Kong's legislative elections, set to take place on December 7, have been suspended.

- Hellish scenes -

Sections of charred scaffolding fell from the burning apartment blocks in hellish scenes late on Wednesday, as flames inside apartments sometimes belched out through windows into a night sky that glowed orange.

Fire services said the wind and drifting debris likely spread the fire from one building to another.

Some of the residents in adjacent blocks who had been evacuated as a precaution were allowed back into their homes on Thursday afternoon.

Crowds moved by the tragedy gathered near the complex to organise aid for displaced residents and firefighters, part of a spontaneous effort in a city that has some of the world's most densely packed and tallest residential blocks.

Volunteers distributed clothes and lunch boxes at the open-air podium of a nearby mall, while a few people gave out flyers with information about missing people.

"It's truly touching," said Stone Ngai, 38, one of the organisers of an impromptu aid station.

"The spirit of Hong Kong people is that when one is in trouble, everyone lends support... It shows that Hong Kong people are full of love."