The US auto safety regulator has opened a probe into whether General Motors' self-driving unit Cruise has taken sufficient precautions with its autonomous vehicles to safeguard pedestrians, it said on Tuesday.

The National Highway Traffic Safety Administration (NHTSA) said its Office of Defects Investigation has received two reports from Cruise of incidents in which pedestrians were injured, and has identified two further incidents via videos posted to public websites.

NHTSA said the reports include Cruise autonomous vehicles "encroaching on pedestrians present in or entering roadways, including pedestrian crosswalks, in the proximity of the intended path of the vehicles".

"This could increase the risk of a collision with a pedestrian, which may result in severe injury or death," the agency added.

A spokesperson for Cruise said the company communicates regularly with NHTSA and "has consistently cooperated with each of NHTSA's requests for information -- whether associated with an investigation or not -- and (plans) to continue doing so".

The probe comes just over two weeks after an incident in San Francisco in which a pedestrian was struck by a hit-and-run driver, thrown into an adjacent lane and hit a second time by a Cruise robotaxi, which was not able to stop in time.

US and California officials have said they were talking to Cruise about that incident.

In August the California Department of Motor Vehicles said it was investigating incidents involving Cruise in San Francisco, after a Cruise robotaxi was involved in a crash with an emergency vehicle.

The California Public Utilities Commission voted in August to allow robotaxis from Cruise and Alphabet's Waymo to operate around the clock, despite strong opposition from residents and city agencies.