- Authorities blame the crash on faulty equipment
- No one was killed in the incident, the company says
- Service has already resumed on the line
Two subway trains collided in a tunnel Tuesday afternoon in downtown Shanghai, injuring more than 260 passengers, according to state media and the subway operator.
State-run Xinhua news agency reported 20 people were in serious condition, and four foreigners were injured but none severely.
Photos of the scene posted on Weibo, China's equivalent of Twitter, showed passengers covered with blood lying on the train or being helped by rescuers.
Shanghai Shentong Metro Company, the city's subway operator, said a train on Metro Line 10 rear-ended another after an equipment failure at a station forced dispatchers to switch to manual mode.
"It's the darkest day since Shanghai Metro began its operations," Shentong said on its official Weibo account, apologizing to all riders and promising a thorough investigation.
One passenger on the first subway described to CNN the frightening moments after his train stalled on the track for about 20 minutes.
"Suddenly we heard this loud noise -- the train started shaking and many people fell to the ground," said Duan Youxing, a recent college graduate. "Smoke came out between two conjoined cars and everyone just panicked."
Local media reported Metro Line 10's signal system was supplied by one of the companies that also manufactured signal equipment for the country's high-speed railway. That company's design flaws were blamed for a fatal bullet train collision in July in eastern China that killed at least 40 people.
Metro Line 10 had another incident less than two months ago. On July 28, a train on the line traveled in the wrong direction and the subway operator later said the accident was caused by a signal system malfunction during an equipment upgrade.
Shanghai, China's largest city, built the world's longest subway network in less than two decades. Shanghai Metro's first line opened in 1995, and now boasts 11 lines and more than 434 kilometers (270 miles) of tracks.
Some experts have long questioned the "great leap forward" strategy in constructing subway systems in cities across China, warning of potential safety issues.
As Shentong restarted running Metro Line 10 Tuesday night, some Chinese netizens responded angrily to the news.
"The injured are still in the hospital and the cause is still being investigated, how dare you announce the resumption of service already -- and with so much pride?" wrote user Liang Shuxin on Weibo. "It only shows the authorities don't consider ordinary people's lives worthwhile."