HONG KONG • At least 18 people were injured in a Mong Kok shopping mall after an escalator suddenly went into reverse at high speed, with a damaged driving chain believed to be one of the main causes of the accident.

The incident at Langham Place on Saturday sent shoppers tumbling down the 45m machine, with at least one of them left in serious condition, reported the South China Morning Post (SCMP).

Preliminary inspections suggest that the driving chain had been damaged and that a braking device had malfunctioned, which caused the upward-running escalator to lose momentum and then begin to run in reverse at high speed.

According to the Electrical and Mechanical Services Department (EMSD), a driving chain couples an escalator's driving gear to the driving wheel of the escalator steps, and if the chain breaks, a safety device is expected to stop the escalator from losing momentum.

"Otis technicians arrived on site at the scene shortly after the incident to assist. Our engineering team and operations leadership are working closely with the EMSD to investigate the cause of the incident," a spokesman said.

"The unit has been shut down for these inspections and will not be returned to service until the cause has been identified and resolved."

It is not clear if the chain of the escalator had come loose or broken.

A Langham Place spokesman said the escalator had not previously undergone any major repair and was inspected last Thursday. No problems were found.

The mall began inspections of all 40 of its escalators on Saturday night to ensure safety. The escalators were still cordoned off yesterday as engineers carried out inspections, reported SCMP.