The blaze, still smoldering early Thursday, has claimed at least 44 lives, with authorities reporting hundreds more remain unaccounted for.

It started on Wednesday afternoon, shocking the financial hub with some of the world's most densely populated and tallest apartment blocks.

Sounds of bamboo scaffolding burning and exploding could be heard at the site. Thick smoke billowed upward from buildings.

"I truly think it's very scary. I am watching it spread from just one building to three, then four," Veezy Chan, 25, a resident of the area, said Wednesday. "It's really terrifying."

Since the shelter opened on Wednesday evening, residents kept arriving to report family members they had lost contact with.

Some sat dazed, looking with reddened eyes at cell phone screens as they hoped for news of missing loved ones.

Social workers distributed blankets and pillows to the elderly to help them endure the nighttime chill.

Shirley Chan, a local resident, called the tragedy terribly sad.

"Imagine a home -- gone, burnt. Anyone would be heartbroken. I can relate to that; it's truly heartbreaking. A home, gone in flames," Chan said. "I can't even put it into words."

A 65-year-old surnamed Yuen said his neighbourhood is home to many elderly residents who use wheelchairs and walkers, and the fire left him and his wife homeless.

He said that since the apartment complex was undergoing maintenance, many residents kept their windows shut -- so they did not hear the fire alarm.

"There is loss of property and loss of life, and even a firefighter has died," Yuen said.

Some citizens have spontaneously donated supplies and delivered them to shelters set up after the fire.

- 'Heart is tingling'-

Logan Yeung, a 29-year-old volunteer, said he would remain on-site to provide support until rescue operations concluded.

"My heart is tingling," he told AFP, adding that he believes construction issues were the cause of the incident.

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

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

But residents nearby said they had never anticipated the flames would spread to other buildings with the wind and burn all night long.

Chan said she "watched the fire burn and couldn't do anything".

"We also didn't know what everyone could do," she said.

City leader John Lee said Thursday that a task force will be set up to investigate the fire and the results will be submitted to the coroner.

The government "needs to provide an explanation to the public," Chan added.