Hong Kong police are investigating whether negligence or criminal elements are involved in the deaths of two repair workers believed to have been locked in an underground tube filled with toxic gas for more than 12 hours over the weekend, the Post has learned.

The investigation on Monday followed allegations suggesting a project manager had abruptly left the construction site in the West Kowloon Cultural District on Saturday morning without completing a safety evaluation while the two labourers were still working in the underground area.

Police officers arrive at the construction site to investigate the death of the two workers. Photo: Jelly Tse

The workers, aged 61 and 63, were supposed to stay on the site from 7am to 6pm on Saturday and they were deployed to the tube at about 10am, according to a source familiar with the case.

Site manager MTR Corporation earlier said the two were repairing seawater cooling pipes linked to the air-conditioning system of the neighbouring Elements shopping centre. The mall was developed and run by the rail giant.

A preliminary investigation suggested the project manager had allegedly left the construction site on Saturday morning without carrying out a safety evaluation, the insider said.

He said the manager returned to the site at about 4pm on Saturday, but could not find the pair.

An engineering staff member also tried to locate the two at around 5pm, but left after discovering the pipe was locked, according to the source.

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The daughter of one of the victims tried to contact her father at about 11pm, but could not reach him.

At about 6.30am on Sunday, she managed to find his colleague, who broke open the locked tube and found the two men unconscious inside, according to the source.

The two workers were later declared dead in hospital.

Officers from the Yau Tsim district crime squad are investigating whether negligence or criminal elements were involved in the death of the workers.

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The source said police would check security camera footage at the site to gather evidence and were trying to find out who had locked the tube.

“Negligence could result in manslaughter,” another source said.

A team of plain-clothes officers on Monday morning went to the site to carry out an investigation.