A dozen students were hospitalized Wednesday after their school bus collided with a pickup truck on a busy southeastern Michigan highway, authorities said.

Two students were in serious condition, Lenawee County Undersheriff Jim Anderson said. The crash happened about 7:15 a.m. Wednesday on U.S. 223 in Rome Township, about 60 miles southwest of Detroit.

Pickup truck driver Tyler Smith, 21, told authorities his view was obstructed by two parked delivery trucks as he pulled out of a gas station into the path of the bus, Anderson said. Smith was in critical condition Wednesday afternoon.

The bus was carrying 25 Onsted Community Schools students, Anderson said, most of them elementary school-age.

District parents were notified about the crash by telephone and email.

Many of the other students had relatively minor injuries, authorities said.

"The majority of the others have been treated and released with minor injuries," said Tedra White, a spokeswoman for ProMedica Bixby Hospital in Adrian.

The bus was partly through with its regular route when it collided with the pickup, Onsted Schools superintendent Mark Haag said.

"The bus was not at fault," Haag said.

The students who weren't injured and the bus driver were taken to school on another district bus. Three of those students later sought medical attention on their own, Haag said.