A "system failure" caused a robotaxi outage involving multiple vehicles operated by Baidu's Apollo Go in central China's Wuhan, local police said on Wednesday, re-igniting safety concerns over the fast-growing service.

Police received reports late on Tuesday that numerous Apollo Go cars had stopped in the middle of roads in Wuhan and were unable to move, according to an official statement.

Passengers were able to exit the vehicles safely and there were no injuries, police said.

The cause of the incident is still under investigation.

At least 100 Apollo Go vehicles were affected, a traffic police officer said in a video published by Shanghai-based news outlet The Paper. The officer added that while the car doors could be opened, some passengers were hesitant to get out because of heavy traffic and called police for assistance.

Local media reported that some passengers were trapped inside the vehicles for nearly two hours.

Baidu did not immediately respond to a request for comment.

The accident sparked renewed discussions on Chinese social media about robotaxi safety and readiness.

An Apollo Go robotaxi carrying a passenger fell into a construction pit in Chongqing in August, and in May one of the cars operated by Pony.ai PONY.Ocaught fire on a road in Beijing. No injuries were reported in either incident.

A widespread power outage in San Francisco at the end of last year also caused Waymo robotaxis to stall and snarl traffic.

Baidu is one of China's largest operators of autonomous driving fleets, alongside Pony.ai and WeRide WRD.O. The companies have rolled out commercial robotaxi services across major Chinese cities and have expanded operations into overseas markets, including the Middle East.

-Qiaoyi Li and Ryan Woo/Reuters