The names of the two crash victims, a 69-year old man, and a 59-year old man, were not immediately released by authorities. The car, a 2019 Tesla Model S, apparently went off the road after being unable to navigate a curve and hit some trees. Herman said the crash is still under investigation and that the exact speed was not yet known. But he said evidence suggests the car was moving at a "high rate of speed."

The Tesla Autopilot feature is designed to assist the driver by keeping the car in a lane of traffic and slowing or stopping the car to avoid obstacles ahead.

"Tesla with Autopilot engaged now approaching 10 times lower chance of an accident than average vehicle," he tweeted.

Musk was referring to company data that showed Teslas with the Autopilot engaged were involved in just one accident for every 4.19 million miles driven in the first quarter of this year, compared to National Highway Traffic Safety Administration data that Tesla said shows one crash in every 484,000 miles for human-operated cars.

But those miles-driven comparisons are not necessarily valid, since the drivers using Autopilot may be more likely to activate it on limited access highways where there is reduced chances of a crash, while the NHTSA data covers all miles driven, including those on local streets with intersections.

Safety concerns

"This tragic crash clearly demonstrates the limitations of advanced driver assistance systems available to consumers today," said NTSB Chairman Robert Sumwalt in a February 2020 report on the 2018 crash in Mountainview, California. "There is not a vehicle currently available to US consumers that is self-driving. Period. Every vehicle sold to US consumers still requires the driver to be actively engaged in the driving task, even when advanced driver assistance systems are activated."

Constable Herman said his department has already been in contact with the NTSB and NHTSA about the crash. It has not been in contact with Tesla as of yet, he said.

Early Monday NHTSA said it has already deployed a Special Crash Investigation team to investigate the crash. Later in the day the NTSB, which is better known for investigating airline crashes, said it is sending two investigators to Texas to conduct a safety investigation looking at both the vehicle's operations and the fire that followed the crash.

The autopilot feature requires the driver's seatbelt to be buckled in order to be engaged. It also is designed to alert the driver if they are not keeping their hands on the wheel often enough.

The crash Saturday resulted in a fire that took firefighters on the scene four hours to put out, using 32,000 gallons of water, according to Herman.

-- CNN Business' Matt McFarland and Peter Valdes-Dapena contributed to this report