U.S. regulators are investigating General Motors' Cruise autonomous vehicle division after receiving reports of incidents where vehicles may not have used proper caution around pedestrians in roadways.

The National Highway Traffic Safety Administration said that the reports involve automated driving system equipped vehicles encroaching on pedestrians present in or entering roadways, including crosswalks. This could raise the risk of a vehicle striking a pedestrian, which could result in severe injury or death, according to the NHTSA.

The NHTSA's Office of Defects Investigation said that it's received two reports involving pedestrian injuries from Cruise vehicles. It's also identified two additional incidents from videos posted to public websites. The office said the total number of relevant pedestrian incidents is unknown. It opened an investigation on Monday.

"Cruise's safety record over 5 million miles continues to outperform comparable human drivers at a time when pedestrian injuries and deaths are at an all-time high," Cruise spokesperson Hannah Lindow said in a prepared statement. "Cruise communicates regularly with NHTSA and has consistently cooperated with each of NHTSA's requests for information –– whether associated with an investigation or not –– and we plan to continue doing so."

The ODI said its investigation is being opened to help determine the scope and severity of the potential problem, including causal factors that may relate to ADS driving policies and performance around pedestrians, and to fully assess the potential safety risks.

In August General Motors' Cruise unit agreed to cut its fleet of San Francisco robotaxis in half as authorities investigated two crashes in the city.

The state Department of Motor Vehicles asked for the reduction at the time after a Cruise vehicle without a human driver collided with an unspecified emergency vehicle.