A woman was struck and killed by one of Uber's self-driving cars in Tempe, Arizona, late Sunday night. This is the first known fatality from an autonomous vehicle accident on a public road.

At the time of the collision, 10 p.m., a vehicle operator was behind the wheel but the car was in autonomous mode, according to Tempe police. No passengers were in the car.

"The vehicle was traveling northbound just south of Curry Road when a female walking outside of the crosswalk crossed the road from west to east when she was struck by the Uber vehicle," the Tempe police said in a statement. "She was transported to a local area hospital where she passed away from her injuries."

The police said Uber is assisting in the still-active investigation. The ride-hailing company has also confirmed that it's temporarily halted its self-driving operations in all other cities where it's been testing its vehicles, including Phoenix, Pittsburgh, San Francisco and Toronto.

"Our hearts go out to the victim's family," an Uber spokeswoman said in a statement. "We are fully cooperating with local authorities in their investigation of this incident."

Uber CEO Dara Khosrowshahi also tweeted his condolences on Monday morning, 

"Some incredibly sad news out of Arizona," he said. "We're thinking of the victim's family as we work with local law enforcement to understand what happened."

Initially, the crash was thought to have been between a bicyclist and the Uber car, according to a report by TV station ABC15, which first reported the accident. 

Most companies working on self-driving cars tout the vehicles as a potentially safer alternative to human drivers. And, for the most part, testing of the technology has shown the cars to be safe. However, this isn't the first time an autonomous vehicle has been involved in a collision. 

Google reported an accident with one of its cars in March 2016 and there have been at least three crashes involving Teslas in autopilot mode, one of which was fatal. Just last week, an Uber self-driving car in Pittsburgh was involved in a collision with another car. With that accident, no injuries were reported but both vehicles had serious damage. 

First published March 19 at 9:07 a.m. PT.
Update, 10:36 a.m. PT: Adds that the victim was a pedestrian, not a bicyclist as initially reported.
Update, 11:07 a.m. PT: Adds comment from Tempe police, Uber spokeswoman and additional background information.
Update, 12:10 p.m. PT: Adds additional background information.
Update, 3:51 p.m. PT: Adds that the crash took place at 10 p.m. Sunday, not early Monday as was initially reported. 

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