Disturbing video has emerged of the moment students were forced to huddle into a corner of their classroom as a gunman fired shots just outside.
The shooting, which took place on Wednesday afternoon (local time) at Marjory Stoneman Douglas High School in Florida, resulted in 17 deaths and at least 20 injuries.
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Traumatic footage from one of the classrooms that escaped unscathed shows the sheer terror of the moment 19-year-old former student Nikolas Cruz unleashed shot after shot in the corridor just metres away.
A number of students can be heard screaming and swearing as the gunfire gets closer.
At the end of the video, a SWAT team arrives in the classroom to escort them out, prompting gasps of relief from the terrified teens.
Cruz had been expelled from Florida's Marjory Stoneman Douglas High School for disciplinary reasons, according to media reports, but he returned to the school to carry out the massacre.