The Boston wreck injured about 10 passengers in an above-ground accident on the city's "T" system near a station in suburban Newton.
A two-car train slammed into the back of another two-car train approaching Woodland Station, said Joe Pesaturo, a spokesman for the Massachusetts Bay Transportation Authority.
"The first one was stopped at a red signal and was ready to proceed to the station when it was struck," he said.
Workers were trying to free the woman who was operating the train that hit the other, and Pesaturo said she appeared to have suffered serious injuries. One passenger was flown to a Boston hospital, and the other injured commuters were taken to nearby Newton-Wellesley Hospital.
The hospital had eight train-wreck patients, none with serious injuries, said spokesman Brian O'Dea.
Passenger Barry Gallup, standing aboard the train that was hit, told WCVB-TV that the impact threw him to the floor.
"I may have been knocked out for a few seconds. ... The next thing I knew I was lying on the ground," Gallup told WCVB.
He described a confused scene immediately after the crash, with some passengers screaming and small fires breaking out on the side of the train.
There was no immediate word on the root cause of the crash, which occurred on a branch of the Green Line, part of the MBTA system serving greater Boston.
