At least 17 students at a Florida high school were killed when a former pupil opened fire on them with an automatic rifle, in what is thought to be the third worst school shooting in US history.
Officials said another 14 were injured at the Marjory Stoneman Douglas High School in the small city of Parkland, around 45 miles north of Miami.
Police identified the gunman as Nikolas Cruz, a 19-year-old former student at who had been expelled for “disciplinary reasons”. Teachers said they had previously been warned that Mr Cruz could pose a danger to the campus.
He was arrested after a brief manhunt.
It was the 18th shooting of the year either in or around school premises, according to research by Everytown for Gun Safety, a non-profit group which advocates for gun control and one of the 10 deadliest mass shootings in US history.
Just as classes were being sent home for the day, police say Mr Cruz began spraying bullets into the high school hallway.
Florida senator Bill Nelson, who claimed to have been briefed by the FBI on the issue, said the shooter wore a gas mask and carried smoke grenades.
He also set off the fire alarm so that his victims would pour out into the hall.
School and University mass shootings in America
“It’s a horrific situation,” Broward County Public Schools Superintendent Robert Runcie told reporters after the shooting. ”It is a day that you pray every day that you never have to see.”
He added: “We didn’t have any phone calls or threats that we know of that were made. We cannot live in a world built on fear, we have do what we can to provide the greatest safety measures for our kids.”
Asked if the incident was related to mental health, Mr Runcie said: “No sane person is going to go and commit such an atrocity.”
Local news reported that a number of people could be seen being loaded into ambulances on a stretcher soon after the shooting.
Other students could be seen running to police safety outside of the school, where they all dumped their backpacks in a pile and were told to sit on the grass.
The school day at Stoneman Douglas typically ends at 2.40pm, and the first tweet from the Broward County Sheriff’s Department about the incident came at 2.53pm.
At around 4.15pm, police said the shooter had been taken into custody after being tracked down without incident.
Jim Gard, a maths teacher at the school who said he taught Mr Cruz last year, told the Miami Herald that teachers had been warned not to let the former student on campus with a backpack.
“There were problems with him last year threatening students, and I guess he was asked to leave campus,” Mr Gard said.
Former classmates also has troubling memories of Mr Cruz.
Jillian Davis, a recent graduate of the high school recalled his “strange talking, sometimes about knives and guns”.
Authorities have confirmed that Mr Cruz was expelled from the school, but have not provided a reason why.
One student was texting with a CBS reporter from inside a closet in the school, and described a chaotic scene.
“All of a sudden there was a really loud noise… people are crying in the closet,” the student said.
Other parents said their children hid in classrooms until they were rescued by armed police in tactical gear.
“My daughter, as of right now, she’s still trapped in a closet. She’s afraid to speak,” a man who identified himself as Caesar Figueroa told the broadcaster. “I told her, ‘Don’t call me, because I don’t want no one to hear your voice.’ So, she’s still trapped in a closet in there.”
Aerial footage from local news showed a number of people lying on the ground outside the school, and being treated for injuries. Meanwhile, dozens of emergency vehicles responded to the scene, including a tank and armed law enforcement.
US President Donald Trump paid tribute to the victims on Twitter.
Sending his “prayers and condolences to the families of the victims”, he later said he was ”working closely with law enforcement on the terrible Florida school shooting.”
Democratic Senator Chris Murphy, a prominent advocate for gun control, addressed the issue on the Senate floor that afternoon, urging his fellow legislators to take action. He had planned to discuss a separate issue, but spoke for several minutes on that day’s shooting.
“This happens nowhere else other than the United States of America – this epidemic of mass slaughter, this scourge of school shooting after school shooting,” said Mr Murphy, who represents the district where the Sandy Hook Elementary School shooting took place in 2012.
He added: “It only happens here not because of coincidence, not because of bad luck, but as a consequence of our inaction. We are responsible.”