A gunman has opened fire inside a hospital in the Bronx borough of New York.
The man, said to be dressed as a doctor, began shooting at the 972-bed Bronx-Lebanon Hospital, reports say.
At least three people are believed to have been shot, although other reports speak of multiple casualties and an ongoing situation.
Messages on social media spoke of doctors and nurses barricading themselves inside the building.
There are some reports of a fire in the building.
New York’s mayor has just been briefed on the situation and police are going floor to floor throughout the hospital looking for the gunman.
The New York Police Department posted a tweet urging members of the public to avoid the area around the hospital at 1650 Grand Concourse.
The New York Times quoted a fire department official as saying that three doctors had been shot. Their condition is not known.
Some reports say the gunman may have been a former employee but this has not been confirmed.
Emergency medical workers cannot yet enter the building as it has not yet been secured by police.
The fire official told the Times one injured doctor was being treated by people inside the hospital using a fire hose as a tourniquet.
The 120-year-old hospital is in the Morris Heights district of the Bronx.