Story highlights School bus driver was not authorized to operate the vehicle

Official: Crash damage is so severe it "looks like a bomb exploded"

(CNN) A nearly empty school bus crossed into oncoming traffic and slammed into a commuter bus in Baltimore on Tuesday morning, killing at least six people, police said.

The school bus, which was blocks away from its first pickup of the day, had no children on board at the time of the crash, Baltimore Police spokesman T.J. Smith told reporters.

The crash, which injured at least 10 people, sheared off the driver's side of the commuter bus, Smith said.

"It literally looks like a bomb exploded in the bus," he said. "It is catastrophic damage."

Fire department and rescue officials at the scene of Tuesday's fatal bus collision.

The school bus rear-ended a car, then sideswiped a cemetery pillar near the road, then crossed into oncoming traffic and collided with the commuter bus around 7 a.m., Smith said.

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