According to the BBC, there are reports of a shooting incident inside a hospital in the Bronx borough of New York.
An armed man said to be dressed as a doctor opened fire 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 shootings and an ongoing situation.
Messages on social media spoke of doctors and nurses barricading themselves inside the building.
Some reports also speak 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.