The US Department of Transportation on Monday opened an investigation into Tesla's Autopilot system, which includes 11 crashes, injuring 17 and killing one individual since January 2018.
The crashes which involve four different Tesla vehicles "have encountered first responder scenes and subsequently struck one or more vehicles involved with those scenes," the department's National Highway Traffic Safety Administration said in a filing.
"Most incidents took place after dark and the crash scenes encountered included scene control measures such as first responder vehicle lights, flares, an illuminated arrow board, and road cones," the filing said.
"The involved subject vehicles were all confirmed to have been engaged in either Autopilot or Traffic Aware Cruise Control during the approach to the crashes," it added.
The regulator's filing covers an estimated 765,000 Tesla vehicles that include Model Y, Model X, Model S, and Model 3 built in 2014-2021.
Tesla's systems are branded under names that include Autopilot, which comes as standard in all newer models.
The California-based firm says on its website Autopilot features are designed to assist drivers, enabling a car to steer, accelerate, and brake automatically within its lane.
Although the company says Autopilot makes Tesla vehicles safer and more capable over time, it notes: "Current Autopilot features require active driver supervision and do not make the vehicle autonomous."
Tesla shares were down 4.5% on the Samp;P 500 as of 12:16 p.m. EDT (1616GMT).