Safety authorities are investigating a fatal crash involving a Tesla Model X vehicle operating in Autopilot mode that caused unprecedented damage.

It comes as increased scrutiny has been placed on semi-autonomous and driverless car technologies after an Uber autonomous car hit and killed a pedestrian in the US last month.

The crash occurred in late March in Mountain View, California. The driver of a Tesla Model X car was travelling on Route 101 when it crashed headfirst into the safety barrier section of a road divider. Two other cars crashed then crashed into the Tesla car, and the car’s battery later caught fire.

The Tesla driver, believed to be a 38-year old male Apple engineer, later died from injuries sustained from the crash.

The National Transportation Safety Board (NTSB) quickly launched an investigation into the crash.

Late last week Tesla confirmed in a statement that the vehicle had been operating in Autopilot mode, but that the driver had ignored warnings to return his hands to the wheel.

“The driver had about five seconds and 150 metres of unobstructed view of the concrete divider with the crushed crash attenuator, but the vehicle logs show that no action was taken,” the company said in a statement.

“The driver had received several visual and one audible hands-on warning earlier in the drive and the driver’s hands were not detected on the wheel for six seconds prior to the collision.”

The NTSB later criticised Tesla for releasing the information while the investigation is still ongoing.

“In each of our investigations involving a Tesla vehicle, Tesla has been extremely cooperative on assisting with the vehicle data,” the NTSB said.

“However, the NTSB is unhappy with the release of investigative information by Tesla.”

Elon Musk responded by tweeting, “Lot of respect for NTSB, but NHTSA regulates cars, not NTSB, which is an advisory body. Tesla releases critical crash data affecting public safety immediately & always will. To do otherwise would be unsafe.”

The crash resulted in unprecedented damage to the vehicle, Tesla said in a blog post.

“We have never seen this level of damage to a Model X in any other crash,” Tesla said.

That stretch of the highway is regularly used by Tesla drivers in the semi-autonomous mode, the company said, with cars using the Autopilot feature safely passing that spot about 85,000 times in the last three years.

The company has blamed the severity of the crash on the safety barrier, which it said was either damaged from a previous crash or too small.

It also said that the car’s battery had worked as designed, and didn’t catch fire until people were out of the way.

“Serious crashes like this can result in fire regardless of the type of car, and Tesla’s billions of miles of actual driving data shows that a gas car in the United States is five times more likely to experience a fire than a Tesla vehicle,” the company said.

The company was investigated by the same safety authority last year following a 2016 fatal crash that saw a Tesla driver die after colliding with a truck. Investigators concluded that while the Autopilot feature had worked mostly as intended, it had given the driver too much leeway in losing focus, and this contributing to the fatal crash.

There has also been increased focus on the safety of driverless cars following the fatal Uber collision in March.