Washington, Safar 02, 1438, November 02, 2016, SPA -- A collision between a school bus headed to pick up children and a commuter bus left six people dead Tuesday, police said in Baltimore, Maryland, according to dpa. There were no children on the school bus when it struck a city commuter bus at 7 am (1100 GMT), authorities said. The school bus is believed to have careened out of control without braking, moments before making what would have been its first morning pickup of a child, and one "working theory" being studied by investigators was that the driver suffered a medical emergency, Baltimore police spokesman TJ Smith said. "It literally looks like a bomb exploded in the bus," he said. Both drivers were killed, including the 33-year-old woman helming the commuter bus. A post mortem examination of the 67-year-old school bus driver was planned with hopes of finding "if there was some kind of pre-existing condition," Smith said. The school bus first rear-ended a car and struck a wall and pillar along a cemetery before veering across the road head-on into the larger commuter bus. A lack of skid marks on the street left by the school bus "leads us to believe there was no deceleration," Smith said. Images from the scene showed the front of the commuter bus heavily damaged and the front of the yellow school bus obliterated. Ten people were injured, including two passengers from the city bus were in critical condition later Tuesday. The commuter bus is believed to have been carrying 13 people including the driver. The driver of the car struck by the school bus suffered minor injuries, as did one aide who was riding on the school bus. Baltimore Police Commissioner Kevin Davis called it a "complicated crash scene." "Obviously, folks who are on a bus at this time of the morning are working folks," he said. "They're on their way to make a living, they're on their way to the job, they're on their way to support their families." Police said the buses have on-board video that could help explain how the crash occurred. --SPA 01:32 LOCAL TIME 22:32 GMT www.spa.gov.sa/w