The White House said President Donald Trump has been briefed about the incident.
Local officials told Miami Herald that the fire department is responding to a mass casualty incident at the high school. They confirmed at least one fatality, the daily said.
"The President has spoken with Governor Scott of Florida and offered federal assistance if needed. Department of Homeland Security Secretary Nielsen also spoke with Governor Scott as well as state and local officials. She has briefed the President on those conversations," White House Press Secretary Sarah Sanders said.