According to CNN and CBS New York, the shooter is believed to be a former employee.
The New York Police Department has responded to an active shooter situation inside a Bronx hospital where at least two people have been shot.
Five other people were wounded in the shooting, and three of those are in serious condition from gunshot wounds, a law enforcement source told CNN.
The 120-year-old hospital has almost 1,000 beds and one of the busiest emergency rooms in New York City.
This is a breaking news story and will be updated with additional information.
Police had yet to secure the area, preventing emergency medical workers from entering, the Times said.
In a radio transmission, police had described the gunman as a tall, thin man wearing a blue shirt and white lab coat.
Police were still trying to identify how many people had been shot; emergency crews had been kept from going inside the hospital while the shooter was a large.
New York Mayor Bill de Blasio was briefed on the shooting and was on his way to the scene, the mayor's Twitter account said.
The 120-year-old hospital is located at 1650 Grand Concourse.