Uber says it has suspended all its self-driving testing after what is believed to be the first fatal pedestrian crash involving its vehicles.
The self-driving testing has been taking place in Phoenix, Pittsburgh, San Francisco in the United States and Toronto in Canada.
Police in the Phoenix suburb of Tempe said one of Uber's self-driving vehicles struck and killed a pedestrian on Sunday night.
Investigators said the vehicle was in autonomous mode with an operator behind the wheel when the woman was hit.
She died in hospital.
Uber chief executive Dara Khosrowshahi expressed condolences on his Twitter account and said the company is working with local police on the investigation.
The federal government has voluntary guidelines for companies that want to test autonomous vehicles, leaving much of the regulation up to states.
The Department of Transportation is considering other voluntary guidelines it says will help foster innovation, but transportation secretary Elaine Chaos has said technology and motor companies need to allay public fears of self-driving vehicles, citing a poll showing that 78 per cent fear riding in them.
The number of states considering legislation related to autonomous vehicles has gradually increased each year, according to the National Conference of State Legislatures.
In 2017 alone, 33 states introduced legislation.
California is among those that require manufacturers to report any incidents to the motor vehicle department during the testing phase. As of early March, the agency had received 59 reports.
Report from Press Association