The US government is investigating reports of Tesla cars braking unexpectedly on motorways.

The so-called “phantom braking” problem is being looked at by US regulator the National Highway Traffic Safety Administration (NHTSA).

It received 354 complaints in the past nine months and its investigation will cover approximately 416,000 Tesla Model 3 and Model Y vehicles from 2021-22.

Drivers say the issue occurs using the Autopilot driver assistance system.

The feature gives the vehicle control over some elements of braking and steering when driving, although it is not a substitute for a human driver.

Despite the name, Tesla recommends drivers remain vigilant and supervise their vehicle, noting the Autopilot ADAS system “does not make the vehicle autonomous”.

Tesla is currently under investigation by the NHTSA over two other matters.