Numerous robotaxis operated by Chinese tech giant Baidu froze in a major city on Tuesday, reportedly trapping passengers inside, stranding them on highways, and causing at least one accident in snarled traffic.

Police in Wuhan confirmed receiving multiple reports of Baidu’s Apollo Go robotaxis stopping in the middle of streets and being unable to move. Police said no injuries have been reported and that preliminary investigations suggest an unspecified “system failure” is responsible for the outage.

Wuhan is a major robotaxi hub for Baidu, which has reportedly deployed more than 500 driverless cars on its roads. It’s unclear how many vehicles malfunctioned. Local news reports cited by Reuters suggest at least 100 robotaxis were affected. Baidu did not immediately respond to The Verge’s request for comment.

The incident has reignited debate over the safety of self-driving cars in China, one of the world’s most enthusiastic adopters of the technology, amid an aggressive global expansion. Baidu is a major operator, deploying robotaxis in 26 cities worldwide, including partnering with Uber in London and Dubai.