Firefighters battled a blaze at a highrise apartment complex in Hong Kong for the second day on Thursday, fire officials said, as the death toll rose to 75 in one of the deadliest blazes in the city’s modern history.

Rescuers holding flashlights were going from apartment to apartment at the charred towers, as thick smoke continued to pour out from some windows at the Wang Fuk Court complex, a dense cluster of buildings housing thousands of people in Tai Po district, a northern suburb near Hong Kong’s border with the mainland.

It was unclear how many people were missing or trapped. Hong Kong leader John Lee said contact had been lost with 279 people early Thursday. Authorities did not provide updates on the missing people or how many were still inside the ravaged buildings during a later news conference.

Video showed rescuers searching in some apartments in the dark. Orange flames were still seen from inside several windows, though the whole complex was now largely a blackened ruin.

Firefighters have been trying to control the flames since midafternoon Wednesday, when the fire was believed to have started in bamboo scaffolding and construction netting, and then spread across seven of the complex’s eight buildings. Fires in four buildings had been effectively put out, with the remaining three towers under control, authorities said Thursday afternoon.

Rescuers are “battling high temperatures and carefully going up floor by floor, thoroughly searching and aiming to rescue people as quickly as possible,” said Wong Ka-wing, deputy director of fire services. “[We] don’t rule out rescuing more injured people.”

One firefighter was among the dead, and 70 people were injured, authorities said. About 900 people were evacuated to temporary shelters overnight.

Rescue worker wheel a woman on a stretcher. One person places an oxygen mask on her face.Authorities suspected some materials on the exterior walls of the highrise buildings did not meet fire resistance standards, allowing the unusually fast spread of the fire. (Chan Long Hei/The Associated Press)Corridor filled with smoke

Resident Lawrence Lee was waiting for news about his wife, who was still trapped in their apartment.

“When the fire started, I told her on the phone to escape. But once she left the flat, the corridor and stairs were all filled with smoke and it was all dark, so she had no choice but to go back to the flat,” he said, as he waited in one of the shelters overnight.

Winter and Sandy Chung, who lived in one of the towers, said they saw sparks fly around as they evacuated Wednesday afternoon. Although they were safe, they were worried about their home.

“I couldn’t sleep the entire night,” Winter Chung, 75, told The Associated Press on Thursday.

Three men, the directors and an engineering consultant of a construction company, were arrested on suspicion of manslaughter. Police have not directly named the company where they work.

“We have reason to believe that those in charge of the construction company were grossly negligent,” said Eileen Chung, a senior superintendent of police.

WATCH | The deadly inferno burned through the night:

3 arrested after Hong Kong highrise fire leaves dozens dead

A fire spread through a dense highrise apartment complex in Hong Kong has left dozens dead and hundreds more reported missing. Three construction company executives were charged with manslaughter, but the cause of the fire remains unclear.

Police on Thursday also searched the office of Prestige Construction & Engineering Company, which The Associated Press confirmed was in charge of renovations in the tower complex. Police seized boxes of documents as evidence, according to local media. Phones for Prestige rang unanswered.

Authorities suspected some materials on the exterior walls of the highrise buildings did not meet fire resistance standards, allowing the unusually fast spread of the fire.

Police also said they found Styrofoam — which is highly flammable — attached to the windows on each floor near the elevator lobby of the one unaffected tower. It was believed to have been installed by the construction company but the purpose was not clear. Secretary for Security Chris Tang said they would investigate the materials further.

The fire started on the external scaffolding of a 32-storey tower, then spread on the bamboo scaffolding and construction netting to the inside of the building and then to the other buildings, likely aided by windy conditions. Firefighters aimed water at the intense flames from high on ladder trucks, but conditions for fighting the fire and rescuing people remained challenging.

A woman cries as she embraces another woman on an urban plaza.About 900 people were evacuated to temporary shelters overnight. (Isaac Lawrence/Getty Images)

A fire safety expert said the incident is “quite shocking,” as regulations in general require buildings to be spaced apart to keep fires from spreading from one building to the next.

“Typically, they don’t spread beyond the building of origin,” said Alex Webb, a fire safety engineer at CSIRO Infrastructure Technologies in Australia, saying the materials police cited could explain why the fires spread.

Hundreds unaccounted for

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 housing complex consisted of eight buildings with almost 2,000 apartments for about 4,800 residents, including many older people. It was built in the 1980s and had been undergoing a major renovation.

Chinese President Xi Jinping expressed condolences to the firefighter who died and extended sympathies to the families of the victims, according to state broadcaster CCTV. He also urged efforts to minimize casualties and losses.

The fire was the deadliest in Hong Kong in decades. In November 1996, 41 people died in a commercial building in Kowloon in a fire that lasted for around 20 hours.