SHENZHEN - At least two people were injured in an escalator accident at a subway station in Shenzhen city, South China's Guangdong province, on Sunday night.

"They have been sent to hospital and doctors said they were free of vital-wound," said Xiao Ping, spokesperson with the Shenzhen branch of the Hong Kong-based Mass Transit Railway (MTR) Corporation, operator of the Shenzhen Subway Line 4, where the accident happened.

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The accident happened at around 9:00 pm at the Qinghu Station, the northern terminal of the south-north subway line in the city that neighbors Hong Kong.

Witnesses told Xinhua that the escalator ran backward, trembling, when the people on it fell down on the ground.

Xiao, however, denied the witnesses' accounts.

"The exact number of the injured and the cause of the accident are both under investigation," said Xiao.

There are not many people in the station as it was not the rush hour, according to witnesses.

Shenzhen now has five metro lines in operation. The 20.5-kilometer-long Subway Line 4 ?opened to operation on June 16. The Qinghu Station is located in an industrial development zone on the Longhua New City Township.

The Hong Kong MTR Corporation also runs the Beijing Subway Line 4, on which the malfunction of an OTIS-produced escalator at a station left one killed and 30 injured on July 5.

A nationwide safety checks on escalators followed the Beijing accident as an requirement of the the General Administration of Quality Supervision, Inspection and Quarantine, China's top quality supervisor.