Passengers pass by an escalator out of service in the Qinghu Station of the Shenzhen Subway Line 4, in Shenzhen City, south China's Guangdong Province, July 11, 2011. The escalator suddenly ran backward causing passengers on it falling down on the ground at around 9:00 p.m. (1300 GMT) Sunday. The accident caused at least two people injured. [Xinhua/Liang Xu]