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A disgruntled former hospital worker armed with a rifle barged into the Bronx Lebanon Hospital Center Friday and opened fire, fatally shooting one doctor and wounding six other people before killing himself, New York City police officials said.

The suspect, identified by sources as 45-year-old Henry Bello, was found dead on the 17th floor of the facility, where he had tried to set himself on fire before he shot himself, according to NYPD Commissioner James O'Neill.

"We've had a real tragedy here," New York City Mayor Bill de Blasio said. "One doctor is dead and there are several more who are fighting for their lives right now."

The mayor did not identify the slain doctor or those who were wounded. O'Neill said five of the wounded were in serious condition and the sixth had been shot in the lower leg.

It was a 911 call at 2:55 p.m. ET that first alerted the NYPD to the unfolding tragedy. The caller said there had been a shooting on the 16th floor of the hospital, O'Neill said.

Henry Bello via Facebook

When police arrived, they discovered "several people had been shot on the 16th and 17th floor by a lone gunman with a long rifle," the commissioner said.

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Then they found the murdered female doctor and the dead gunman, who was wearing a white medical-type coat, on the 17th floor, O'Neill added.

Bello had brought along gas and matches and had tried to ignite a fire near the nurses station, a senior officials with direct knowledge of the investigation told NBC News. It was doused by the hospital's sprinkler system.

The hospital was placed on lockdown as police launched a floor-by-floor search for any possible accomplices.

The gunman went to the 16th floor looking for a specific doctor, that doctor was not there and he began shooting others apparently at random, a senior police official said.

Of the six injured, five are staff of the hospital and one is a patient, Sridhar Chilimuri, physician-in-chief at Bronx Lebanon Hospital, told reporters. The five injured staff members are in critical condition and the injured patient is very stable, he said. Most of the wounded staff will require more surgeries, he said.

Chilimuri was one of the physicians who went upstairs to evacuate patients. "People are emotional, yet they have to move fast. You have cops everywhere with guns drawn," he said. "It’s tough, but I'm very proud. We did what we need to do."

A hospital staff member outside the Bronx-Lebanon Hospital as they respond to an active shooter in New York on June 30, 2017. Timothy A. Clary / AFP - Getty Images

Bello was armed with what multiple senior NYPD officials said was an AR-15 type assault rifle.

"That's a type of weapon that you so often see in these types of situations," NYPD Police Commissioner Bill Bratton told MSNBC.

Just before 4 p.m., J. Peter Donald, assistant commissioner for communication for the NYPD, announced the search for the suspect was over.

"One shooter is deceased at the hospital," he said.

The FBI announced in a tweet a little over an hour later that "there is no nexus to terrorism."

NYPD is handling Bronx shooting. At this time there is no nexus to terrorism; we are monitoring situation. @NYPDnews — FBI New York (@NewYorkFBI) June 30, 2017

De Blasio called the shooting a "horrific situation unfolding in the middle of a place that people associate with care and comfort" and said that doctors and other medical staff protected each other and patients amid the chaos.

"Our hearts go out to the family of the doctor who passed away and we're in both our hearts and our prayers standing in solidarity with the families of all of those who were wounded and all of those who are fighting for their lives right now," the mayor said.

Chilimuri described the wounded hospital staffers as family medicine physicians, medical students, family medicine residents, and a specialist in gastroenterology.

Diana Cruz, practices administrator to the hospital's cardiology practice, described how staff closed the doors and secured patients after the hospital sounded a "code silver" alert, which is used to warn if someone has a gun or knife.

"I heard someone coming through the stairwell, I looked to see who it was, it was a wounded physician who I know very well," Cruz told NBC New York. Staff assessed his wounds and whisked him to the emergency department.

"It was autopilot. There was no time to think," Cruz said. "Although there was an active shooter, we just proceeded to do what we do every day."