Updated at 4:35 p.m. ET
The Broward County, Fla., school superintendent Robert Runcie, says there are fatalities in the shootings at Marjory Stoneman Douglas High School in the city of Parkland, northwest of Fort Lauderdale.
In a tweet, Broward County Sheriff Scott Israel said there are "at least 14 victims." He did not specify whether they are injured, dead, or some combination of the two.
The school was locked down as some students were escorted outside while others were being advised to remain barricaded inside.
Authorities have not determined a motive for the shooting.
Florida Gov. Rick Scott as well as President Trump have been told about the shooting.
This is a developing story. Some things that get reported by the media will later turn out to be wrong. We will focus on reports from police officials and other authorities, credible news outlets and reporters who are at the scene. We will update as the situation develops.