A malfunctioning shopping centre escalator left 18 people injured, one seriously, after it suddenly changed direction on Saturday (25 March).

The 45-metre moving staircase at Hong Kong's Langham Place mall was travelling upwards when it suddenly began to move down. It quickly increased its speed, sending shoppers tumbling to the bottom.

Video footage of the event showed a crush at the entrance to the escalator as people fell on top of one another. Others grappled with the handrails for balance and even tried to jump on to the adjacent staircase.

One man suffered a head injury and was in a serious condition in hospital, police said. The other people hurt suffered less serious injuries and their conditions were described as stable, the South China Morning post reported.

Eyewitness Lau Kit-ying told the newspaper: "It was so sudden that people couldn't respond in time."

She said saw a man bleeding among those people crushed at the bottom.

"I'm not sure if he was conscious, but a foreign man and a few mall staff helped stop his bleeding with a first aid kit," Ms Lau said. "But most of the injured were young people and they stood up quickly… I'm glad that there weren't any elderly people involved."

Several eyewitnesses said the escalator was travelling at least twice as fast as normal.

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A preliminary investigation indicated a broken drive chain may have caused the accident. But the escalators had passed an inspection just two days before the incident.

The mall has asked the Otis Elevator Company, who are contracted to provide and maintain the machinery, to look into what went wrong.

The government has ordered engineers to run tests on all escalators in the city longer than 15 metres and promised legal action if failure to adhere to regulations caused the accident.