A school bus and a passenger bus collided in downtown St. Louis (search) on Friday, sending them crashing onto the grounds of a historic courthouse and injuring three adults and about a dozen children.

One of the victims was a man walking his dog, struck by one or both of the buses. He was in critical condition; his dog was killed. Both bus drivers also were injured.

The injured children appeared to suffer mostly cuts and bruises. Paramedics initially treated them in the lobby of a bank near the accident scene. Another school bus took the children to hospitals for evaluation, Fire Department Capt. Kim Bacon said.

The accident happened at about 7:15 a.m. in front of the Old Courthouse, built in the mid-19th century and now a historic monument. Both buses smashed through a wrought-iron fence around the building.

Police aren't sure what caused the accident, but some witnesses, including Clarissa McCray, 12, a student on the school bus, said the Metro bus ran a red light.

"Next thing I know the driver was on the ground," McCray said. "Kids were panicking, crying."

Only two passengers were on the Metro bus, and they were not injured, Metro spokeswoman Adella Jones said. The driver's window shattered and she suffered cuts and glass in her eye, Jones said.

Twenty-four students were on the bus, bound for Margaret Buerkle Middle School (search) in south St. Louis County. City students are bused to the suburban school as part of a voluntary desegregation program.

Bruce Ellermann, a spokesman for the desegregation program, said all of the children were taken to hospitals to be checked out, even though half of them did not appear to be injured. All 24 were expected to be out of the hospital by the end of the day.