The death toll in a fire that engulfed several high-rise apartment buildings in Hong Kong has risen to at least 36, authorities say, with more than 275 others still unaccounted for.

Hong Kong leader John Lee confirmed the updated death toll early on Thursday, hours after flames first took hold in apartment blocks in Tai Po, a district in the northern part of the city, on Wednesday afternoon.

Lee told reporters that at least 279 people were still unaccounted for while 29 were hospitalised, including seven in critical condition.

Firefighters worked into the night as thick, black smoke billowed from the 31-storey towers and orange flames lit up the sky at the Wang Fuk Court estate.

Nine people had been declared dead at the scene, the Fire Services Department said earlier in the day, while local media reported that some residents were believed to be trapped inside the buildings.

The fire department had upgraded the blaze to a level five alarm – the highest level – after nightfall.

Chan Derek Armstrong, deputy director of Hong Kong’s Fire Services Department, told reporters on Wednesday that the fire spread rapidly and authorities received numerous calls for help from residents.

“Debris and scaffolding of the affected buildings are falling down, so [that poses] additional danger to our frontline personnel,” he said, adding that high temperature inside the buildings posed a challenge for the emergency responders.

“It’s quite difficult for us to enter the buildings and go upstairs to conduct firefighting and rescue operations,” he said.

‘People trapped inside’

“There’s nothing that can be done about the property. We can only hope that everyone, no matter old or young, can return safely,” a Tai Po resident surnamed So, 57, told the AFP news agency near the scene of the fire.

“It’s heartbreaking. We’re worried there are people trapped inside.”

Reporting from Tai Po on Wednesday, journalist Laura Westbrook told Al Jazeera that when the fire started, it spread through bamboo scaffolding that was affixed to the buildings in the housing estate.

Frames of scaffolding were seen tumbling to the ground as firefighters battled the blaze, while scores of fire engines and ambulances lined the road below the development, witnesses told Reuters.

“As I’ve been standing here, I can smell the smoke and occasionally we hear these pops, as some of the debris falls to the ground,” Westbrook said.

Wang Fuk Court is one of many high-rise housing complexes in Hong Kong, a city that is one of the most densely populated areas in the world.

Harry Cheung, 66, who has lived at Block Two in one of the complexes for more than 40 years, said he heard “a very loud noise” at around 2:45pm local time (06:45 GMT) and saw a fire erupt in a nearby block.

“I immediately went back to pack up my things,” he told the Reuters news agency. “I don’t even know how I feel right now. I’m just thinking about where I’m going to sleep tonight because I probably won’t be able to go back home.”

Dozens of ambulances, fire trucks

People had gathered on a nearby overhead walkway, watching in dismay and taking pictures as smoke billowed from the buildings.

Firefighters deployed 128 fire trucks and 57 ambulances to the scene.

Meanwhile, authorities set up a casualty hotline and opened two temporary shelters in nearby community centres for evacuated residents. Sections of a nearby highway also were closed by the firefighting operation.

“Residents nearby are advised to stay indoors, close their doors and windows, and stay calm,” the Fire Services Department said in a statement on Wednesday. “Members of the public are also advised to avoid going to the area affected by the fire.”

Tai Po, located near the border with mainland China, is an established suburban district with a population of about 300,000 people. Records show the housing complex consisted of eight blocks with almost 2,000 apartments housing about 4,800 people.