Uber Technologies Inc. has halted autonomous vehicle tests after one of its cars struck and killed a woman in Tempe, Arizona, in what is likely the first pedestrian fatality involving the technology.

The 49-year-old woman, Elaine Herzberg, was crossing the road outside of a crosswalk when the Uber vehicle operating in autonomous mode under the supervision of a human safety driver struck her, according to the Tempe Police Department.

After the incident, which happened at 10 pm local time on Sunday, she was transferred to a nearby hospital, where she died from her injuries.

"Uber is assisting and this is still an active investigation," Liliana Duran, a Tempe police spokeswoman, said in an emailed statement.

Uber said on Monday that it was pausing tests of all its self-driving vehicles on public roads in Pittsburgh, San Francisco, Toronto and the greater Phoenix area.

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

Companies including Alphabet Inc., General Motors Co., Uber and Baidu Inc. are investing billions of dollars to develop autonomous-vehicle technology because it has the potential to transform the auto industry, transportation in general and the way cities work.

One analyst has estimated Alphabet's Waymo unit is worth at least $70 billion. The fatality in Tempe could slow testing, delay commercialization and undermine such optimism.

Testing has expanded to complex urban areas as states like Arizona and Texas take a light-touch regulatory approach and companies race to be first to commercialize the technology.

That's helped improved the systems, but also increased the chance of a pedestrian death. Experts have long worried about the impact deadly crashes could have on the nascent industry.

"We're within the phase of autonomous vehicles where we're still learning how good they are. Whenever you release a new technology there's a whole bunch of unanticipated situations," said Arun Sundararajan, a professor at New York University's business school.

"Despite the fact that humans are also prone to error, we have as a society many decades of understanding of those errors."

The National Transportation Safety Board is opening an investigation into the death and is sending a small team of investigators to Tempe, about 10 miles east of Phoenix.

The Department of Transportation's National Highway Traffic Safety Administration dispatched a special crash investigation team.

The NTSB opens relatively few highway accident probes each year, but has been closely following incidents involving autonomous or partially autonomous vehicles. Last year, it partially faulted Tesla Inc.'s Autopilot system for a fatal crash in Florida in 2016.

The NTSB's cautionary tone on the emergence of self-driving technology contrasted with the Department of Transportation, which revised its policy on self-driving vehicles last year in an attempt to remove obstacles to the testing of such vehicles.

"As always we want the facts, but based on what is being reported this is exactly what we have been concerned about and what could happen if you test self-driving vehicles on city streets," said Jason Levine, executive director of the Center for Auto Safety, a Washington-based advocacy group.

"It will set consumer confidence in the technology back years if not decades. We need to slow down."

The Phoenix area is a fertile ground for experiments in the technology. Uber has been testing there with safety drivers behind the wheel.

Late last year, Alphabet Inc.'s Waymo, which has tested in the Phoenix area for years, began removing the safety drivers to transport a small number of residents. (Waymo staff sit in the back seat.)

General Motors Co. is also testing in the Phoenix area. A GM spokesman declined to comment, and a representative from Waymo didn't return multiple requests for comment.

"Public safety is our top priority, and we are in communication with law enforcement, which is investigating the accident and gathering facts, as well as Uber," a spokesman for Arizona Governor Doug Ducey said.

Uber has had incidents in the past. Last year, Uber suspended its self-driving car program after one of its autonomous vehicles was involved in a high-impact crash in Tempe.

The Uber vehicle was not responsible for the incident, and there were no injuries, the police said at the time.

"Tempe has been supportive of autonomous vehicle testing because of the innovation and promise the technology may offer," Tempe Mayor Mark Mitchell said in a statement on Monday.

"Testing must occur safely. All indications we have had in the past show that traffic laws are being obeyed by the companies testing here. Our city leadership and Tempe Police will pursue any and all answers to what happened in order to ensure safety moving forward."

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This article was originally published by Bloomberg.