A doctor opened fire inside a New York City hospital where he used to work, killing one and wounding six others before turning the gun on himself, law enforcement officials said.

Police officers found the gunman, identified as Henry Bello, dead of a self-inflicted gunshot wound on the 17th floor of Bronx-Lebanon Hospital, New York City Police Commissioner James O’Neill said on Friday.

Forty five-year-old Bello, who was wearing a white lab coat, was armed with an assualt rifle besides carrying ID. The body of a woman was found close to the gunman’s body, CNN reported.

Six persons were wounded, of which five are in serious condition and are “fighting for their lives”, O’Neill said, adding that several of the wounded were doctors at the hospital.

The hospital’s fire alarm system went off during the siege, apparently because the shooter tried to set himself on fire, the Police Commissioner said.

So far authorities have not offered a motive. The FBI said the shooting did not appear to be an act of terrorism. New York Mayor Bill de Blasio called it an act of work-related violence.

The shooting began at 2.50 p.m. (local time) at the 120-year-old hospital, which claims nearly 1,000 beds spread across multiple units. Its emergency room is among the busiest in New York City.

Police went floor by floor searching for the shooter while the hospital had been surrounded by emergency response vehicles.

A ‘red alert’ went off within the hospital, which was placed on lockdown. Doctors and nurses barricaded themselves within.

“I barricaded the door with an IV machine, two chairs and my whole bed,” a 23-year-old patient said.