Authorities cordon off an escalator that malfunctioned Wednesday at Jing'an Temple Station, leaving 13 people injured. Photo: Cai Xianmin/GT

Thirteen people were injured Wednesday when an escalator at Jing'an Temple Station suddenly changed directions.

The upward-moving escalator's drive chain snapped around 8:20 am, according to a microblog post by Shanghai Shentong Metro Group, the city's metro operator.

"The escalator paused for a short while and then began to move in the opposite direction," a witness surnamed Wang told the Global Times.

Many passengers fell and some tried climbing back up the escalator, said Wang, who was taking the stairs when the escalator malfunctioned.

Metro employees responded immediately and sent the injured people to a hospital, according to the operator's post.

One passenger suffered serious injuries and remained under observation Wednesday afternoon. The rest got away with bruises. Five of the injured had left the hospital by Wednesday afternoon.

The escalator was manufactured by Guangzhou Otis Elevator Co Ltd in Guangdong Province. The company conducted maintenance on the escalator on July 26. Its next maintenance visit was scheduled for August 20.

Otis expressed its condolences for the injured in a statement on its microblog around 4 pm. It said it is willing to offer help to the injured. It also said it would conduct an investigation into the accident in cooperation with the government.

Shanghai Shentong plans to examine all of the escalators in the city's metro stations.

Wednesday's malfunction was not the first time metro passengers were injured on an escalator. On November 7, 2003, 10 people were hurt after an escalator at Xinzhuang Station on Line 1 suddenly changed directions, the Youth Daily reported.

Many accidents have happened in China on escalators made by Otis, the US escalator manufacturer.

Five passengers were seriously injured after an Otis escalator suddenly changed directions on December 21, 2007, at Century Avenue Station on Line 4. On July 11, 2011, an Otis escalator suddenly stopped at Caoyang Road Station on metro Line 3, though no one was injured, according to a report on the news portal xinmin.cn.

On July 5, 2011 in Beijing, one passenger died and three others suffered serious injuries after an Otis escalator suddenly changed directions at Beijing Zoo Station on metro Line 4, the Xinhua News Agency reported.