An unknown technical problem caused a number of robotaxis owned by the Chinese tech giant Baidu to freeze on Tuesday in the middle of traffic, trapping some passengers in the vehicles for more than an hour.

In Wuhan, a city in central China where Baidu has deployed hundreds of its Apollo Go self-driving taxis, people on Chinese social media reported witnessing the cars suddenly malfunction and stop operating. Photos and videos shared online show the Baidu cars halted on busy highways, often in the fast lane.

A college student in Wuhan tells WIRED that she was stuck in a Baidu robotaxi with two friends for about 90 minutes on Tuesday. (She asked to be only identified with her last name, He, to protect her privacy.) The student says the car malfunctioned and stopped four or five times during the trip before it eventually parked in front of an intersection in eastern Wuhan. Luckily, it was not a busy road, and the group was not in immediate danger. The screen display in the car asked the passengers to remain in the car with seatbelts on and wait for a company representative to come “in five minutes,” according to a photo He shared with WIRED.

He says it took about 30 minutes to reach a Baidu customer representative on the phone. “They kept saying it would be reported to their superior. But they didn’t explain what caused [the outage] or let us know how long we needed to wait for the staff to come,” He says. But no one ever came, and after another hour of waiting, the three passengers decided to just get out and go home by themselves (the doors weren’t locked).

On Chinese social media, other passengers also complained about being unable to reach Baidu’s customer support. “I tried every way I could think of to call for help using the options the app showed, but the phone line wouldn’t go through, and when I pressed the SOS button it told me it was unavailable. So then what exactly is the SOS for?” wrote one person in a post on RedNote alongside a video showing the button not working. She said she had to force the door to open and get out of the car as traffic halted to a complete stop behind her robotaxi. “Apollo Go, you really owe me an apology,” she wrote.

Baidu didn’t immediately respond to a request for comment. Local police in Wuhan issued a statement around midnight in China that said the situation was “likely caused by a system malfunction,” but the incident is still under investigation. No one was injured, and all passengers have exited the vehicles, the police added. It’s unclear how many of Baidu’s robotaxis may have been impacted.

One dashcam recording posted to RedNote shows a car passing 16 Apollo Go vehicles parked on the road in the span of 90 minutes. On several occasions, the video shows the driver narrowly avoiding hitting the robotaxis by braking or changing lanes at the last minute.

Others were apparently not as fortunate. In another RedNote post, a man claimed he crashed into one of the malfunctioning Baidu vehicles. The man wrote in the caption that he was driving over 40 mph on a highway when the car in front of him suddenly changed lanes to avoid the stopped robotaxi. He couldn’t react fast enough and ended up running into the self-driving car. Photos of the man’s orange SUV being towed away show that the car’s front-right fender was completely torn off, and other parts appeared to have sustained major damage.

There were at least two other collisions on the same day, according to photos and videos posted on Chinese social media. A RedNote user in Wuhan confirmed to WIRED that she drove past a white minivan that had gotten into a rear-end collision with a parked robotaxi. The back of the Baidu car was badly damaged, but the two people standing beside the scene looked unharmed, she says. She added that she estimates she also saw at least a dozen more parked robotaxies.

Baidu is one of China’s leading self-driving firms. The company has launched robotaxi services in over a dozen Chinese cities so far and recently began expanding internationally to places like Seoul, Abu Dhabi, and Dubai. In February, Baidu announced that it completed 20 million rides covering over 300 million kilometers (about 186 million miles).

Wuhan has been among the most aggressive cities in allowing Baidu's fully autonomous vehicles on public roads. It permits them to operate on highways and run trips to the airport.