A shooter identified as a former student has opened fire in a Florida high school, killing multiple people and sending hundreds of panicked students fleeing into the streets while others huddled in classrooms.
Dozens of police swarmed Marjory Stoneman Douglas High School in Parkland, about 72 kilometres north of Miami after the attack before they took the suspected shooter into custody on Wednesday afternoon.
"There are numerous fatalities. It's a horrific situation," Broward Country Schools Superintendent Robert Runcie said.
He said the alleged perpetrator used to attend the school and is believed to be 16 years old.
He said the school district had gotten no warning of a potential shooter and that there was no evidence of more than one shooter.
"We have at least 14 victims," the Broward County sheriff's office said on Twitter. It did not make clear if that number included people who were wounded in addition to the dead.
Students hid in classrooms until they were rescued by police in tactical gear, friends and family members said.
McKenzie Hartley, 19, who identified herself as the sister of a student at the school described the scene in a text message: "She heard him shooting through the windows of classrooms and two students were shot."
Panicked parents checked on their children.
"It is just absolutely horrifying. I can't believe this is happening," Lissette Rozenblat, whose daughter goes to the school, told CNN.
Her daughter called her to say she was safe but the student also told her mother she heard the cries of a person who was shot.
"She was very nervous. She said that she could hear the person who was shot crying out for help," she told CNN. "My daughter is safe and I am very grateful."
Live television showed dozens of students, weaving their way between law enforcement officers with heavy weapons and helmets, and large numbers of emergency vehicles including police cars, ambulances and fire trucks.
Florida Governor Rick Scott said on Twitter that had he had been in touch with local officials about the incident.
The school had recently held a meeting to discuss what to do in such an attack, Ryan Gott, a 15-year-old freshman told CNN.
"My prayers and condolences to the families of the victims of the terrible Florida shooting," US President Donald Trump said on Twitter.
"No child, teacher or anyone else should ever feel unsafe in an American school."