The Labour Department on Sunday said it is investigating a fatal incident in which two construction workers died after apparently inhaling gas while working underground.

The two men, in their 60s, were pulled from a construction site on Austin Road at about 8am on Sunday.

They were taken to Queen Elizabeth Hospital where they were certified dead.

The son of one of the workers, surnamed Lau, said he is angry about the lack of supervision during the construction.

"Supposedly the company should have our phone numbers... But we weren't notified until the police knocked on our door three hours after the incident," Lau told RTHK.

Siu Sin-man, chief executive of the Association for the Rights of Industrial Accident Victims, described the case as "unacceptable".

She said it is understood that they were repairing an MTR pipeline, adding that the railway company should give an explanation as soon as possible.

"We think the incident is outrageous. There is no reason for sending two workers to work underground without considering their safety. How do they get out? There should be some procedures in place. If it is a confined space, sufficient protective gear should be provided," she said.

In response, the MTR said it is highly concerned about the incident and will launch an investigation.

It said the two workers were working on the replacement of cooling pipes for the air-conditioning system of the Elements shopping mall.