Firefighters took 12 minutes to free two unconscious female workers trapped in the wreckage of the scaffolding.

The two, aged 54 and 68, were rushed to United Christian Hospital in Kwun Tong, but were later pronounced dead.

Three other employees, a man and two women, were taken to Queen Elizabeth Hospital in Yau Ma Tei for treatment.

The woman who was working on the scaffolding suffered injuries to her legs and chest and was said to be in a serious condition on Tuesday night.

The Labour Department said she was installing aluminium plates and glass when the scaffolding collapsed.

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Chief Inspector Kwok Ching-yee of the Kowloon East regional crime unit said officers would work with other departments and talk to experts to establish the cause of the tragedy.

“If human error is determined to be a factor, police will initiate a criminal investigation and pursue prosecution,” she added.

Fay Siu Sin-man, the chief executive of the Association for the Rights of Industrial Accident Victims, said the workers at the foot of the scaffolding were cleaning company staff and on a break when the scaffolding fell.

One of the dead women was said to be on her first day back at work after the Lunar New Year holiday.

The main contractor, Hip Hing Construction, told the media that it would investigate the incident and offer help to the families of the victims.

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Siu questioned whether the accident was related to the truss-out bamboo scaffolding design and emphasised the need for strict risk assessment of the structures, especially after a long holiday.

“It is crucial to evaluate whether the truss-out scaffolding can be used in a certain manner and whether its load-bearing capacity is sufficient,” Siu said. “These are the aspects that need to be thoroughly considered.”

The Labour Department added the main contractor had inspected the scaffolding structure last Wednesday when work resumed at the site after the Lunar New Year break.

The department said it had launched its own investigation and officials said there had been no previous serious incidents or deaths at the site.

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“The investigation will focus on the design, installation, utilisation, and inspection of the scaffolding,” a spokesman from the department added.

The Labour Department also said it had issued suspension notices to the contractors, suspending the erection, alteration, dismantling and use of bamboo scaffolds on the external walls of the building at the construction site.

The contractors could not resume the work process until the department was satisfied that measures to abate the relevant risks had been taken.

The Buildings Department said the main contractor was expected to examine all other scaffolding on the site on Wednesday.

Pano Harbour is a 582-flat development by China Resources Land (Overseas) and Poly Property Group.

Fame Well Creation, a joint venture by the two companies, said it was shocked by the incident and expressed its condolences to the families of the victims.

The company said it had told the contractor to carry out a thorough investigation and give suitable support to the affected workers.

It added the contractor would cooperate fully with the government investigation.

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A fire broke out on bamboo scaffolding at a building on the site in November last year.

More than 100 workers were evacuated to the rooftop and to ground level. No one was injured.

The fire was extinguished in about 40 minutes. Investigators said it was thought the sparks from welding work had set fire to the scaffolding net.

Flat sizes range from 371 square feet to 4,850 square feet and construction is expected to be completed this year.