The use of the malfunctioned escalator is suspended.

An escalator accident left at least four injured at a subway station in Shenzhen City, south China's Guangdong Province, on June 10, 2011, the Guangzhou Daily reported.

The accident took place at around 9:00 p.m. at the Qinghu Station, the northern terminal of the south-north subway line in Shenzhen.

The injured are under medical treatment in hospital and are in stable condition, according to the subway operator, the Shenzhen branch of the Hong Kong-based Mass Transit Railway (MTR) Corporation.

Witnesses claimed the escalator ran backward when the people on it fell down on the ground, but the subway operator denied the accounts.

The cause of the accident is still under investigation.

Shenzhen now has five subway lines in operation. The line where the accident took place is Subway Line 4. It opened to operation on June 16.

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

China’s top quality supervisor, the General Administration of Quality Supervision, Inspection and Quarantine, has launched a nationwide safety checks on escalators.