The US state of California is easing its rules for autonomous car testing, by allowing testing of vehicles in which there is no human driver.

The new rules have yet to be submitted for public consultation, with a final version expected by the end of the year, according to its Department of Motor Vehicles (DMV).

"These rules expand our existing autonomous vehicle testing program to include testing vehicles where no driver is present," said DMV Director Jean Shiomoto.

"This is the next step in eventually allowing driverless autonomous vehicles on California roadways."

California took some heat earlier for seeking to stop testing of fully autonomous cars -- those in which a human is not physically on board.

Rules proposed at the end of 2015 required that a person with a permit always be present in the vehicle, and be able to regain control of it. And that person would be held responsible for traffic offenses or accidents.

The Federal Road Safety Agency NHTSA, however, differed a few months later saying that a computer system -- based on the artificial intelligence of autonomous cars -- could be considered their "driver."

California, and Silicon Valley in particular, is a key location for automakers and tech startups working on driverless cars. The change should help keep that the case.

The DMV says it has permitted 27 manufacturers to test self-driving cars.