A 19-year-old gunman has opened fire at a Florida high school he was previously expelled from, killing 17 people before he was arrested.
The violence erupted at Marjory Stoneman Douglas High School in Parkland, about 72 kilometres north of Miami.
Live television footage showed students streaming out of the building as dozens of police and emergency services personnel swarmed the area.
The gunman was identified as Nikolas Cruz, who previously attended the school and was expelled for unspecified disciplinary reasons, Broward County Sheriff Scott Israel said.
“It’s a horrific situation,” Broward Country Schools Superintendent Robert Runcie told reporters separately.
The gunman surrendered to police without a struggle, Israel said.
“It’s catastrophic,” he said. “There really are no words.”
Twelve of the dead were killed inside the school building, two others just outside, one more on the street and two other victims died of their injuries at a hospital, Israel said.
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He said the victims comprised a mixture of students and adults.
“There was a time when he did attend the school,” Israel said. “I don’t know why he left, I don’t know when he left.”
It was the 18th shooting in a US school so far this year, according to gun control group Everytown for Gun Safety.
Staff and students told local media that a fire alarm went off around the time the shooting started, sparking chaos as some 3,000 students at the school first headed into hallways before teachers herded them back into classrooms, to seek shelter in closets.
Kyle Yeoward, a 16-year-old junior, said he was in the bathroom on the second floor of the building on the campus where most of the shooting took place, when he heard two shots.