Authorities said firefighters had entered the basement area of the site on Wednesday to inspect and fight the blaze.

They added drones were deployed for aerial surveillance and robots were sent to assist firefighters.

“We have changed the firefighting strategy from defensive to proactive since noon today,” Lee Koon-yau, assistant director of the Fire Services Department’s New Territories North, said.

“Firefighters need to continue to conduct risk assessments and proceed step by step. For now, our firefighting work is expected to continue for some time.”

Lee said tackling the fire was a problem because of the large area of the site, 70 metres by 80 metres, as well as the smoke and high temperatures.

He added the basement was like a maze and contained a large number of wooden boards and building materials.

Lee said 20 highly flammable oxyacetylene cylinders were found at the site, but added they were stable and not an explosion risk.

He added a total of 167 fire engines, 12 ambulances and more than 580 firefighters and ambulance personnel had been involved in dealing with the fire by 5pm on Wednesday.

He added the cause of the blaze was still under investigation.

Emergency responders could earlier only fight the No 4 alarm fire, from the periphery and fly drones to conduct inspections. Fires in Hong Kong are rated on a scale of one to five, with five the most serious.

Two tower cranes at the site, measuring 60 metres and 70 metres tall, were not at an immediate risk of collapse, Mary Chan Yuen-ming, chief officer at the Buildings Department, said.

She added the assessment was based on their base support structures as well as the temperatures at the location. Chan added the department would conduct more checks later to decide when construction work could restart.

Emergency personnel were first alerted to the fire at the site on Hung Nga Road at 1.20pm on Tuesday. It was upgraded to a No 3 alarm fire at 2.44pm and again at 9.31pm on Tuesday to a No 4 alarm.

The Fire Services Department on Tuesday said explosions had occurred in the basement, possibly due to oxyacetylene cylinders.

Nearby residents were advised to close their doors and windows and stay calm.

Plumes of thick, white smoke still rose from the site at about 10am on Wednesday.

Housewife Yeung Wan-saa, 39, who lives on the 14th floor of Hung Foon House at the nearby Hung Fuk Estate, said an abnormal smell lingered in her home although she had shut the windows and doors.

“At first, it smelled like something burning. Then it turned into a pungent and unpleasant smell,” she said, adding that she had to turn on an air purifier hoping that the smoke would not affect her three-year-old child’s health.

Blaze at Hong Kong construction site leaves 2 tower cranes at risk of collapsing

Chan Lan, 47, who also lives in the public housing estate, said it was her first time witnessing such a big fire. As her flat was not facing the fire, she said the smoke indoors was manageable after she closed the windows.

“I am not that worried because I see many fire trucks and firefighters coming. I believe they are doing their job,” she said.

Construction worker Chan Wai-kit, 70, said he was at his office in the building next to the fire. At about 5pm on Tuesday, he and his colleagues were asked by firefighters to leave the building.

He said he arrived at the scene at about 8am on Wednesday, hoping to get back to work but found the building was closed off.

“We are still waiting for our manager to give further arrangements,” he said.

Fire at Hong Kong’s New Lucky House kills at least 5, injures 35

The site is for a Housing Society dedicated rehousing estate at Phase 2 of the Hung Shui Kiu/Ha Tsuen New Development Area.

The scheme was expected to be completed in 2026 and provide 962 subsidised flats for sale.

James Chan Yum-min, the chief executive officer of the Housing Society, said it had ordered contractor Paul Y. Engineering to suspend work at the site, where construction is at an early stage.

He added that the society would consider reinforcing the two tower cranes, or disassembling and replacing them, after the site was reopened.

The contractor told the Post it had quickly evacuated workers from the site on Tuesday and would continue to monitor the situation and cooperate with the authorities’ investigation into the incident.