A railroad source told the Chicago Tribune both trains were in motion when at least two cars of the Burlington Northern express from Aurora, Ill., struck the Amtrak train around 8:15 a.m. The source said the investigation will concentrate on switches.
At least 10 ambulances rushed to the scene to aid passengers, including a woman pregnant with twins who went into labor, said passenger David Dahler.
Passenger Kirk Musselman said: "It was pretty abrupt. As we turned, the cars were sticking out and they struck the engine of the other train."
Metra spokesman Tom Miller said at least two train cars were damaged. Service on lines using the south end of the station was halted until 10 a.m.