An early-morning fire severely damaged a vacant building on the grounds of McLean Hospital in Belmont, but no patients at the world-famous behavioral health facility were affected by the public safety emergency, the hospital said.

The fire was discovered around 2:40 a.m. by Belmont police officers who smelled smoke while patrolling the area, town officials said. Firefighters were called to battle what eventually became a two-alarm fire that required mutual aid from surrounding fire departments.

In a statement, hospital administrators said the building was known as the Codman Building and was not in use.

“Thanks to the Belmont Fire Department’s rapid response, the fire was contained to that one building and no other areas of the McLean campus were affected,” the hospital said.


The hospital said patients on the McLean campus, which offers inpatient care, were safe.

“Since it was a closed building located in a remote area of the McLean campus, no evacuations were needed and no patient care services were disrupted,’’ the hospital said in a statement.

The cause of the fire is under investigation.

Police posted a video of the fire on Twitter about 4 a.m. Monday.

Fire crews from Cambridge, Watertown, and Arlington also responded.

Some photos of the scene posted Twitter:

john R. Ellement contributed to this report.