CAMBRIDGE, Mass. (AP) — Transit police in Boston were investigating a shooting on a subway platform near Harvard University on Sunday that prompted the school to issue a shelter-in-place order for students and staff.

Authorities rerouted passengers on part of the city’s subway system to shuttle buses as officers from various departments searched for a suspect.

Richard Sullivan, superintendent of the Massachusetts Bay Transit Authority Transit Police Department, said in an email that a man armed with a gun fired approximately four to five rounds at a “targeted individual” while on the southbound platform at the Harvard Square station, according to a preliminary investigation. The suspect then fled the station.

There is no evidence the targeted person or anyone else was injured, he said.

Police were alerted to a report of shots fired around 2:15 p.m. A message was later sent to the Harvard community, urging people to shelter in the nearest building until further notice and that police were searching the area around the busy station, which is near the school’s main campus in Cambridge.

The message, which was posted on Harvard’s website, was removed later Sunday afternoon.

After delaying trains in the area, the MBTA announced it had decided to replace service there with shuttle buses due to “police activity.” Passengers were warned they could experience delays as the shuttles were being dispatched.