Only the central carriages derailed, leaving one auto bent nearly into an L shape across the tracks. It happened just before 07:00 (06:00 GMT).
Cause of the crash is still being investigated.
Trenord, the railway company operating the commuter trains, has halted services between Milan and Treviglio.
Two cars peeled off the rails and came to rest at an angle.
Helicopters were taking the injured to nearby hospitals.
Witnesses said the train trembled for a few minutes before the accident. Since then, the woman said there has been no reply on her daughter's telephone.
According to the reports, fire fighters were seen gathering in the coach trying to evacuate the injured passengers.
Italian media quoted witnesses as saying the train began to shake heavily as if it was travelling over rocks.
The Milan prosecutor's office has opened an official investigation into the incident.
Trenord, a local train organization serving the Lombardy area, has a famous reputation among riders. He denied any common cause between Thursday's derailment and a July 23 derailment outside the Pioltello station in which no one was injured.