A Pan AM Railways train struck a 10-year-old boy who officials said was trespassing on the tracks at the Fitchburg MBTA station about 6:30 p.m. Friday.
The boy was "critically injured," according to police, and was taken to a nearby hospital for emergency care. There was no word Monday on his condition.
The Pan AM train traveling west on MBTA-owned tracks consisted of three locomotives and several cargo cars, transit police said.
An investigation is underway.