June 6: An escalator moving up at Kavi Subhash (New Garia) station of Metro Railway suddenly stopped and reversed its direction this morning, throwing off commuters and leaving at least five injured.

None of the injured needed to be hospitalised but the accident sent shivers down the spine of countless Calcuttans who take Metro everyday.

The freak incident could have ended in a disaster as the steel plates of an escalator can inflict fatal injuries to children and the aged.

Metro spokesperson Indrani Banerjee said a multinational firm headquartered in Germany, Thyssenkrupp, was in charge of the maintenance of the 76 escalators across the 24 Metro stations.

"The escalators were last checked on May 14. We have asked for a report about the incident from the firm. Strict action will be taken if any wrongdoing is found," Banerjee told Metro.

When this newspaper called up Thyssenkrupp's office in Calcutta, a person who identified himself as an executive of the firm said a spokesperson would call back at the earliest.

The company later issued a statement saying: "The cause of the incident at this point is unknown and is being thoroughly investigated. Our team is cooperating fully with these investigations and the relevant authorities."

The escalator near the stationmaster's cabin, which leads up to the platform from where Dum Dum-bound trains leave, abruptly stopped for a few seconds around 11am before moving downward. Witnesses said around 20 commuters were on the escalator.

Prahlad Mondal, who was towards the bottom of the escalator, fell on the floor and injured his right elbow and right knee. Moumita Pyne, 29, escaped a fall by clinging on to a handrail but her right feet started bleeding after it hit a steel plate.

The injured commuters were taken to the stationmaster's office, where they were given first-aid.

The Metro spokesperson said at least five persons were injured.

The Kavi Subhas accident was a rerun of what had happened at Girish Park station two years ago. Several commuters were injured in that accident and two of them - a couple - had to be admitted to hospital.

The 2015 accident had prompted Metro to order an overhaul of all escalators.

"An escalator gets its power supply from three phases - one results in clockwise movement, another in anticlockwise movement and the third stops the stairs by making them neutral," an engineer said. "An alteration in the supply phase could lead to an incident like the one that happened at Kavi Subhas station."

The direction of an escalator can also be changed by operating a switch.

A professor of electrical engineering at IIT Kharagpur said a fault in the electronic circuit could lead to a change in the supply phase.

A probe into the Girish Park accident revealed that a bolt in a chamber containing the escalator motor had come off accidentally, reversing the direction of the stairs.