Hong Kong - Hong Kong firefighters are scouring scorched high-rises Thursday for over 250 people listed as missing, a day after the financial hub's worst blaze in decades killed scores of people in an apartment complex.

Over 24 hours after fire broke out in the eight-building housing estate with 2,000 units, flames were still visible in some windows as crews sprayed water on the blackened exteriors.

Authorities have begun investigating what sparked the disastrous blaze, including the presence of bamboo scaffolding and plastic mesh wrapped around the structures as part of construction work.

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

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

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

Multiple residents of Wang Fuk Court, located in Hong Kong's northern district of Tai Po, told AFP that they did not hear any fire alarm and had to go door-to-door to alert neighbors 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 neighbors, telling them to leave – that's what the situation was like," added.

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

But the toll continues to increase, with the latest number rising to 65 as of Thursday evening local time.

Among the dead was a 37-year-old firefighter, who was found with burns on his face half an hour after losing contact with colleagues, according to the fire service director Andy Yeung.

Lee said in the early hours of Thursday that 279 people were still unaccounted for, though firefighters said later that they had established contact with some of those people. Authorities have not updated the figure since.

Chinese President Xi Jinping expressed condolences to the victims, including "the firefighter who died in the line of duty", according to state media.

Deadly fires were once a regular scourge in densely populated Hong Kong, especially in poorer neighborhoods.

However, safety measures have been ramped up in recent decades and such fires have become much less commonplace.