Seventeen people have been killed in the mass shooting at a high school in Parkland, Florida, authorities confirmed.
Broward County Sheriff Scott Israel told reporters that 12 victims died inside the school, three victims died outside, and two died in the hospital after a lone gunman opened fire at Marjory Stoneman Douglas High School. Another 14 to 18 people were injured.
Doctors for the Broward Health North hospital system, where the victims were treated, said three people were still in critical condition.
School district superintendent Robert Runcie called the shooting – one of the 10 deadliest in US history – "a horrific situation".
"It is a horrible day for us," he told reporters.
Authorities have identified the suspect as 19-year-old Nikolas Cruz, a former student at the school. Mr Israel said the suspect had been expelled before the shooting for "disciplinary reasons". The sheriff's office is still combing through Mr Cruz's online activity, which Mr Israel said included some "very disturbing" content.
Teachers at the school told the Miami Herald that they had been warned not to let Mr Cruz onto school grounds, as he had been flagged as a potential threat. Mr Runcie, however, said he was not aware of any threats from the former student.
Mr Cruz was arrested off-campus about an hour after the shooting, Mr Israel said. Authorities believed he used an AR-15 rifle and multiple magazines to carry out the massacre.
Witnesses said a fire alarm went off at the same time the shooting commenced at the high school on Wednesday afternoon, shortly before classes were to be dismissed. Students ran into the hallway before teachers pulled them back inside.
One teacher, Melissa Falkowski, told CNN she pulled 19 students into a closet with her to protect them. They waited 40 minutes for the shooting to stop.
Another student told WSVN 7 that she saw the shooter gun down her teacher as he opened the door to let students inside. The door was left swinging open as the students cowered inside.
"As he walked by the door was open," the student, identified only as Alex, said. "He could have walked in at any time, and we just had to be as quiet as possible."
Several parents learned of the shooting from their children, who sent them panicked text messages from inside the building. Students were eventually escorted out of the building by SWAT teams to be reunited with their families.
The shooting is the 18th school shooting in the US this year, according to gun control advocacy group Everytown for Gun Safety. It was the sixth where students were wounded or injured.
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