Hong Kong's deadliest fire in years burned through the night, leaving at least 44 people dead and 279 reported missing with rescuers still pulling residents from blazing high-rise apartment buildings into the morning.

Several local media outlets reported that police had arrested three men on suspicion of manslaughter in connection with the fire which began Wednesday afternoon in a housing complex in Tai Po district, a suburb in the New Territories.

By Thursday morning local time, the fire was yet to be put out and rescues continued with the death toll reaching 44. Hundreds of residents were evacuated as the fire spread across seven of the eight buildings in the complex.

At least 29 others remained in hospital. Bright flames and smoke shot out of windows as night fell.

Authorities said earlier that investigators would be looking into factors including whether material on the exterior walls of high-rise buildings met fire resistance standards, as the rapid spread of the fire was unusual.

Officials said the fire started on the external scaffolding of one of the buildings, a 32-storey tower, and later spread to inside the building and then to nearby buildings, likely aided by windy conditions.

Chinese leader Xi Jinping on Wednesday expressed condolences to a firefighter who died and extended sympathies to the families of the victims, according to state broadcaster CCTV.

He also urged efforts to minimise casualties and losses. The fire at three of the buildings was "coming under control" shortly past midnight, according to the Fire Services Department.

The housing complex consisted of eight buildings with almost 2,000 apartments housing about 4,800 residents, including many elderly people.

It was built in the 1980s and had recently been undergoing a major renovation. Fire chiefs said high temperatures at the scene made it difficult for crews to mount rescue operations.

A column of flames and thick smoke rose as the blaze spread quickly on bamboo scaffolding and construction netting that had been set up around the exterior of the buildings.

About 900 people were evacuated to temporary shelters. Authorities said that hundreds of firefighters, police officers and paramedics were deployed.

Firefighters aimed water at the intense flames from high up on ladder trucks.

The blaze, which started mid-afternoon, was upgraded a level five alarm - the highest level of severity - as night fell.

Authorities said that conditions remained very challenging for firefighters.

"Debris and scaffolding of the affected buildings (is) falling down," said Derek Armstrong Chan, deputy director of Fire Service operations.

"The temperature inside the buildings concerned is very high. It's difficult for us to enter the building and go upstairs to conduct firefighting and rescue operations."

The fire department said it received "numerous" calls requesting assistance and that some residents remained trapped as of Wednesday night.

Firefighters deployed more than 140 fire trucks and more than 60 ambulances to the scene.

The dead included a 37-year-old firefighter, while another received treatment for heat exhaustion, director of Fire Services Andy Yeung said.

District officials in Tai Po have opened temporary shelters for people left homeless by the fire.

"I've given up thinking about my property," a resident who only provided her surname, Wu, told local TV station TVB.

"Watching it burn like that was really frustrating."

Tai Po is a suburban area in the New Territories, in the northern part of Hong Kong and near the border with the mainland Chinese city of Shenzhen.

Bamboo scaffolding is a common sight in Hong Kong at building construction and renovation projects, though the government said earlier this year that it would start phasing it out for public projects because of safety concerns.

The fire is the deadliest in Hong Kong in years.

In November 1996, 41 people died in a commercial building in Kowloon in a level five fire that lasted for around 20 hours.