Calcutta, Dec. 17: A moving escalator at Calcutta Metro's Girish Park station reversed its direction, throwing off commuters late this evening and injuring nine.

At least two of them needed hospitalisation. Eyewitnesses said the escalator, which opens on Central Avenue, stopped abruptly at 8.33pm and within a few seconds started moving downwards. Several people were caught off guard and could not maintain their balance.

There were at least 12 passengers, who had got off a Dum Dum-bound train and were headed for the exit near Liberty Cinema, on the escalator when the snag happened. This exit has no stairs.

Poltu Chakraborty, 32, suffered head injuries while Paresh Daripa, 47, was left nursing deep cuts on his right thigh and left toe. Both were taken to Calcutta Medical College and Hospital and from there to the railways' BR Singh Hospital in Sealdah.

Chakraborty, a Jorabagan resident, said: "When the escalator stopped abruptly, I caught the handrail. But it started moving downwards and I couldn't keep my balance." His head banged on the sharp edge of a stair. Some other commuters fell on him.

Daripa, 47, who works and lives in Burrabazar, fell on another passenger and a sharp edge of the escalator pierced his left toe and right thigh. He received four stitches on the toe and a bandage on the thigh.

Metro has ordered a probe. The escalators are repaired and maintained by a private agency with whom it has an annual contract.

"The escalator was operating normally when I stepped onto it. But within seconds it stopped. All of us leaned forward and almost at the same moment, it started moving downwards. We lost our balance," said S.P. Singh, a resident of Jorabagan who had boarded the train from Chandni Chowk.

"I could see at least three passengers, including a girl, thrown into the air. They landed after a few somersaults," Singh said.

He alleged that the Metro authorities did not provide first aid to the passengers. "They said there was no antiseptic available. So we wet a piece of cotton in water and put it on a man's wound to stop the bleeding."

An engineer said an escalator received electric supply from three phases. One makes it move clockwise, another anti-clockwise with the third neutral. When an escalator is in the neutral phase, it stops moving.

The same escalator can be made to move either clockwise or anti-clockwise through a switch. Only trained personnel are supposed to operate the switch.

"Tonight at the Girish Park station, the supply phase may have altered, which led to the reversal of direction," said a professor of electrical engineering at Jadavpur University.

"It may also happen if the drive that is used to set the speed of the escalator malfunctions," he added.