Police say 17 people were killed when a gunman armed with at least one rifle and multiple magazines opened fire at Marjory Stoneman Douglas High School in Parkland north of Miami on Wednesday.
Choking back tears as he called for tighter gun control laws, counter-terrorism analyst and former FBI agent, Phil Mudd told CNN: "A child of God is dead.
"Cannot we acknowledge in this country that we cannot accept this?
"Just pray for this city; pray for this school, the parents, the folks that lost their lives."
Officers confirmed 19 year old suspect Nikolas Cruz, who had attended the school prior to being expelled for disciplinary reasons, had been arrested and taken into custody.
There were frantic scenes of people fleeing from school buildings, as paramedics rushed to treat the injured.
US President Donald Trump tweeted: "My prayers and condolences to the families of the victims of the terrible Florida shooting.
"No child, teacher or anyone else should ever feel unsafe in an American school."
The shooting, which started at around 2.30pm-local time, sent the site in lockdown. Students and teachers were told to stay barricaded in their classrooms.
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