An escalator travelling upwards suddenly ran in reverse and 12 people were slightly injured in the Jing'ansi subway station, state-run Xinhua news agency reported.
The Otis escalator passed an annual inspection in July 2013, and the next check should have been in August this year, said Shanghai municipal quality inspection department.
Specific causes will be identified after technical appraisal and investigation.
Injured passengers were taken to hospital and the operator suspended use of escalators in the station. Escalator accidents have happened in China before.