US transport authorities are to investigate after a driver was killed in a Tesla driving on Autopilot mode.

A Tesla statement said: "What we know is that the vehicle was on a divided highway with Autopilot engaged when a tractor trailer drove across the highway perpendicular to the Model S. Neither Autopilot nor the driver noticed the white side of the tractor trailer against a brightly lit sky, so the brake was not applied.

"The high ride height of the trailer combined with its positioning across the road and the extremely rare circumstances of the impact caused the Model S to pass under the trailer, with the bottom of the trailer impacting the windshield of the Model S.

"Had the Model S impacted the front or rear of the trailer, even at high speed, its advanced crash safety system would likely have prevented serious injury as it has in numerous other similar incidents."

The manufacturer's Autopilot system is currently in 'beta' development phase, disabled by default, and requires drivers to keep their hands on the wheel at all times.

This is the first death involving the Autopilot system, according to Tesla.