A self-driving Uber car hit and killed a pedestrian as she was crossing the road in the first fatality involving the controversial fleet of autonomous vehicles.
Elaine Herzberg, 49, was hit by an SUV around 10pm on Sunday in Tempe, Arizona, when she was walking her bicycle outside of a crosswalk.
She was immediately rushed to the hospital where she died from her injuries, ABC 15 reported.
Tempe Police say the SUV was in autonomous mode at the time of the crash but that a vehicle operator was also behind the wheel.
The accident is the first time a pedestrian has been killed on a public road by an autonomous car, which has been praised as the safer alternative to a traditional car.
In a statement, an Uber spokesperson said the company is aware of the incident and is "fully cooperating with local authorities in their investigation".
Uber CEO Dara Khosrowshahi offered his condolences to the victim's family on Twitter on Monday afternoon, and reiterated that the company will be working with local law enforcement to figure out what happened.
The ride-share service has since paused its self-driving car operations in Pittsburgh, Phoenix, San Francisco and Toronto.
Tempe Mayor Mark Mitchell released a statement on Twitter on Monday afternon in support of the halt.
He wrote: "The City of Tempe has been supportive of autonomous vehicle testing because of the innovation and promise the technology may offer in many areas, including transportation options for disabled residents.
"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.
"I support the step that Uber has take to temporarily suspend testing in Tempe until this event is fully examined and understood. That is a responsible step to take at this time."
This is not the first time Uber has grounded its fleet of self-driving cars. In March 2017, an autonomous Volvo SUV got into accident when the other vehicle "failed to yield" while making a left turn, according to police.
"The vehicles collided causing the autonomous vehicle to roll onto its side. There were no serious injuries," Tempe police spokeswoman Josie Montenegros said at the time.
The only known death involving a self-driving car and a driver was when Tesla driver Joshua Brown was killed in 2016 while operating the company's Autopilot software.
However, this crash occurred only after Brown ignored repeated warnings to put his hands back on the steering wheel.
Tesla has stated that Autopilot is a driver assistance feature, not a replacement for a human driver.
The US National Highway Traffic Safety Administration and the National Transportation Safety Board said on Monday that it will be sending teams to Tempe to investigate the accident.
In a statement, the NHTSA said it is "in contact with Uber, Volvo, federal, state and local authorities regarding the incident" and will take appropriate action.
Meanwhile, other states are already taking action. California regulators ordered Uber to stop its newly launched self-driving car service in San Francisco until it gets a state permit.
In a letter obtained by The Associated Press, DMV officials wrote that Uber "must cease" deploying the cars or face unspecified legal action.
Uber knew about the permit requirement but argued that its cars do not meet the state's definition of an "autonomous vehicle" because they require a person behind the wheel to monitor and intervene if needed.
In September, US Transportation Secretary Elaine Chao released new guidelines that permit more testing of self-driving cars and address regulation between the federal government and states.
Chao argued that self-driving technology could also improve mobility for the elderly, disabled and other restricted populations.
But the non-profit Consumer Watchdog has warned that roads are being turned "into private laboratories for robot cars with no regard for our safety."
Not much information has been released about Herzberg. However, she has been arrested six times between October 2014 and October 2015 for a number of drug charges and probation violations.
Additionally, according to her Facebook account, she has been married three times and became a mother at age 15 and again at age 18.