LITCHFIELD, Ill. (AP) — A school bus carrying 6th-grade students from the St. Louis area has collided with a tractor trailer near the southern Illinois community of Litchfield.

Authorities say the accident Monday afternoon, which injured an unknown number students, as the bus was headed back to Grantfork Upper Elementary School in Highland from a field trip to the state Capitol in Springfield. Highland is located near St. Louis.

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Police say the bus rear-ended the truck seven miles north of Litchfield on Interstate 55. One student was airlifted to a hospital in Springfield with serious injuries. The driver of the bus was also reported seriously injured.

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Authorities say at least seven students were taken to St. Francis Hospital in Litchfield with non-life threatening injuries.

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