A self-driving car being tested by Google struck a public bus on a Silicon Valley street a minor accident that appears to be the first time one of the tech company's vehicles caused a crash during testing.

Google accepted at least some responsibility for the collision which occurred on February 14 when one of the Lexus SUVs it has outfitted with sensors and cameras hit the side of the bus near the company's headquarters in Mountain View California.

No one was injured according to an accident report Google wrote and submitted to the California Department of Motor Vehicles. It was posted online on Monday.

According to the report Google's car intended to turn right off a major boulevard when it detected sandbags around a storm drain at the intersection.

The right lane was wide enough to let some cars turn and others go straight but the Lexus needed to slide to its left within the right lane to get around the obstruction.

The Lexus was going 3kph when it made the move and its left front struck the right side of the bus which was going straight at 24kph. The car's test driver - who under state law must be in the front seat to grab the wheel when needed - thought the bus would yield and did not have control before the collision Google said.

While the report does not address fault Google said in a written statement "We clearly bear some responsibility because if our car hadn't moved there wouldn't have been a collision."

Chris Urmson the head of Google's self-driving car project said in a brief interview that he believes the Lexus was moving before the bus started to pass.

"We saw the bus we tracked the bus we thought the bus was going to slow down we started to pull out there was some momentum involved" Urmson told The Associated Press. He acknowledged that Google's car did have some responsibility but said it was "not black and white".

The Santa Clara Valley Transportation Authority said none of the 15 passengers or the driver of the bus was injured.

The transit agency is reviewing the incident and hasn't reached any conclusions about liability spokeswoman Stacey Hendler Ross said in a written statement.

There may never be a legal decision on fault especially if damage was negligible - as both sides indicated it was - and neither Google nor the transit authority pushes the case. Still the collision could be the first time a Google car in autonomous mode caused a crash.

Google cars have been involved in nearly a dozen collisions in or around Mountain View since starting to test on city streets in the spring of 2014. In most cases Google's cars were rear-ended. No one has been seriously injured.

Google's written statement called the February 14 collision "a classic example of the negotiation that's a normal part of driving - we're all trying to predict each other's movements".

Google said its computers have reviewed the incident and engineers changed the software that governs the cars to understand that buses may not be as inclined to yield as other vehicles.