Media playback is unsupported on your device Media caption Hong Kong escalator malfunction injures dozens

Two technicians in Hong Kong have been arrested for "perverting the course of justice", after a malfunctioning escalator injured shoppers in a mall.

The two men were suspected of tampering with the escalator after the incident, report local media.

An escalator at the Langham Place shopping centre suddenly reversed at high speed on Sunday, sending passengers tumbling down.

The reason behind the malfunction is still unknown.

Why were the men arrested?

Officials had called in the two technicians, who work for Otis Elevator Company, to assist in investigations hours after the incident.

The escalator had been shut down and all personnel involved in the investigation were ordered not to touch it.

Late on Sunday night however, officials discovered that the escalator's auxiliary braking system had been reactivated, reported local media. Newspaper Apple Daily said the reactivation could have affected the escalator's computer data records.

Officials ordered police to arrest the two men on the spot.

Otis has expressed surprise at the arrests and said it would seek clarification from authorities.

What happened with the escalator?

At least 18 people were injured when the escalator, which was going up at Langham Place, suddenly changed direction and started going down at a fast pace.

Videos of the incident show dozens of people losing their balance and tumbling down. Several are seen piled up at the foot of the escalator, with one man lying unconscious on the floor.

Two people are still in hospital and are in a stable condition.

The city government has ordered immediate tests on all escalators which span more than 15m (45 feet) in height.

Why did it happen?

There has been no official explanation yet, but city officials said a damaged driving chain within the escalator, and a malfunctioning braking device, may have caused the incident.

Escalator engineer Charles Wong told the South China Morning Post that auxiliary brakes should have kicked in if the main brakes had failed, and that it was rare for a driving chain to break.

The mall said that the escalator had last been inspected on Thursday, with no problems detected.