A MARC train unloading passengers at Washington’s Union Station was hit by a MARC locomotive about 10 a.m. on Thursday as it was trying to couple with the train to take it into the station’s rail yard.

A dozen people were evaluated and seven were taken to the hospital with minor injuries, according to D.C. fire department spokesman Alan Etter. The injuries were mostly neck and back soreness, and Etter said he expected patients would be treated and immediately released.

The force of the impact caused one set of wheels on one of the train’s coaches to derail, Amtrak spokeswoman Tracy Connell said.

Connell said MARC train No. 419, which had arrived from Baltimore on the Penn Line, was unloading passengers at Union Station’s upper level when the accident occurred.

“As people were getting off, the MARC locomotive was backing up to couple to the train. It was kind of like it was rear-ended,” Connell said. “It was a light locomotive used to take a train to the yard. We don’t know the extent of the impact.”

She added that Amtrak won’t know the cause of the crash until it completes an investigation.

MARC spokeswoman Cheron Wicker said trains leaving D.C. would be delayed into the evening.

Capitol Police and Amtrak Police were on the scene. Traffic reopened outside Union Station at 12:15 p.m.

— Daniel Heim