"One doctor is dead, and there are several doctors who are fighting for their lives right now amongst those who are wounded", Mr de Blasio said. The body of a woman was found close to the gunman's body, CNN reported.
Bello, 45, shot dead a woman, on the 17 floor and injured at least six others on the 16 floor, before killing himself the New York Police Department (NYPD) Commissioner James O'Neil, said.
They say Bello then shot himself, and staggered, bleeding, into a hallway where he collapsed and died with the rifle at his side.
Police went floor by floor searching for the shooter while the hospital had been surrounded by emergency response vehicles. On Saturday morning, four victims were stable and two were critical.
It was reported Friday afternoon that a gunman shot multiple people at Bronx-Lebanon Hospital in New York City.
He had other troubles including a listing as a respondent in a California divorce in 2002 and was also arrested for "fare evasion on the New York subway system".
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Some people believed that the death toll would have been higher had the shooting occurred anywhere in the hospital.
Six people were wounded on the 16th floor, and five - who are hospital staff members - are in serious condition from gunshot wounds. He apparently attempted to set himself on fire before shooting himself, O'Neill said.
The authorities is currently carrying out its investigation.
He said Bello, who worked at night as a doctor, sent him a threatening email after he was fired. His emergencies are among the busiest in New York City.
The names of the victims of Friday's shooting were not released.
In his email to The News, Bello blamed two doctors by name for getting the ax.