At least 17 people have died after a gunman opened fire at the Marjory Stoneman Douglas High School in Parkland on Wednesday afternoon.
Authorities responded to reports of a shooting at about 2.30pm.
The suspect was identified as 19-year-old Nikolas Cruz. He was arrested at the scene and taken into custody. Sheriff Scott Israel, of Broward County, said Cruz was a former student at the school who was previously expelled for disciplinary reasons.
The sheriff said the gunman had at least one AR-15 rifle as well as multiple magazines.
He told reporters that an attack began outside the school.
Twelve people were found dead inside the building, two were found just outside the school and another was found dead in a nearby street. A further two people died later while receiving medical treatment.
Sixteen injured people were taken to hospital - the two who later died among that number.
US president Donald Trump tweeted his condolences saying: "No child, teacher or anyone else should ever feel unsafe in an American school."