PHOENIX -- Arizona authorities say six people were killed after a passenger bus was clipped by another vehicle and rolled over on the interstate south of Phoenix.

Department of Public Safety spokesman Bart Graves says 15 others, including two 11-year-olds, were injured in the Friday morning accident on Interstate 10 about 25 miles south of Phoenix. The bus was carrying 21 passengers.

Graves says 10 of the injured were taken by ambulance to various hospitals and five were flown by medical helicopter.

He says two adult males and four adult females were killed.

The commercial bus is owned by Tierra Santa Inc. out of Los Angeles.

Graves says it's not clear where the bus was headed.

Rescuers set up a triage area in the middle of the interstate and broke out windows of the bus to get to victims.