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.

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 the police for assistance.

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

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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 caught 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. ​

The companies have rolled out commercial robotaxi ​services across major Chinese cities and have expanded operations into overseas markets, including the ​Middle East.