BOSTON -- Police were investigating reports that two people were slightly injured in an MBTA Green Line collision early Tuesday morning, but T officials later said no one was hurt in the incident.

Two trains traveling about 5 mph were traveling inbound near the Boylston MBTA stop when one hit another about 9:10 a.m., MBTA spokeswoman Lydia Rivera said.

The collision was described as one car "tapping" another, and one of the cars sustained minor damage, T officials said.

There was nothing to indicate any problems with signals or equipment and the driver of the second trolley has indicated she was at fault, the MBTA said.

No cellphones or handheld electronic devices were involved, according to the MBTA.

Four MBTA employees on the two trolleys have been taken out of service and will undergo drug and alcohol testing as is routine after such incidents.

Tuesday's collision was under investigation. Trains were evacuated and taken out of service. There were about 200 people on board at the time, Rivera said.

Service was interrupted for about 15 minutes, she said.