US president Donald Trump has said Wednesday's mass shooting turned a Florida school into a "scene of terrible violence, hatred and evil".
Mr Trump was speaking a day after the shooting that killed at least 17 people.
Mr Trump said the entire nation “with one heavy heart” was praying for the victims and their families.
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My little brother just sent me this video of the swat team evacuating his classroom at stoneman douglas. So scary but glad he's safe. @nbc6 @CBSMiami @NBCNews @wsvn @CBSNews pic.twitter.com/XNTtra221q
— Melody (@Melody_Ball) February 14, 2018
#BSO is working a developing incident regarding a report of active shooter located at 5901 Pine Island Rd, Parkland. Here's what we know so far: deputies are responding to reports of a shooting at Stoneman Douglas High. There are reports of victims. PIO will be on scene 3:15pm.
— Broward Sheriff (@browardsheriff) February 14, 2018
Avoid the area of Stoneman Douglas HS. #BSO is currently working a developing incident regarding a report of active shooter.
— Broward Sheriff (@browardsheriff) February 14, 2018
He said no child should have to go to school fearing for their lives.
Mr Trump said he would travel to Florida to meet with victims’ families, explore how to better secure schools and “tackle the difficult issue of mental health”. The president was silent on the issue of gun control.
Suspect Nikolas Cruz is due to appear in court later on Thursday having been charged with 17 counts of premeditated murder.
The incident happened at Marjory Stoneman Douglas High School in Parkland, a town about 50km north of Fort Lauderdale, shortly before 3pm as the school day was coming to a close.
Among the victims of the attack are Aaron Feis an assistant football coach at the school. A further 16 people died while another 15 were injured.
Authorities in Florida have confirmed that schools in the area have received copycat threats in the wake of the attack.
In an update on the investigation, Broward County Sheriff Scott Israel said that threats had been received and authorities were treating them seriously.
Ron Runcie, superintendent of schools in Broward County said that grief counsellors were on site at the school and other schools in the area. “Every minute of the day we are focusing on how we can support our families, our students and our staff as we work through this horrific situation.”
He said: “Now is the time for this country to have a debate about sensible gun control.”
Just before the shooting broke out, some students thought they were having another fire drill.
Such an exercise had forced them to leave their classrooms hours earlier. So when the alarm went off Wednesday afternoon shortly before they were to be dismissed, they once again filed out into the hallways.
That was when police say Mr Cruz, equipped with a gas mask, smoke grenades and multiple magazines of ammunition, opened fire with a semi-automatic weapon.
Thousands of students were evacuated from the school after the attack took place, some carried out in stretchers.
Frantic parents rushed to the school to find Swat team members and ambulances surrounding the huge campus and emergency workers who appeared to be treating the wounded on pavements. Students who had not run began leaving in single-file with their hands over their heads as officers urged them to evacuate quickly.
Most of the fatalities were inside the building, though some victims were found fatally shot outside, the sheriff said.
It was the nation’s deadliest school shooting since a gunman attacked an elementary school in Newtown, Connecticut, more than five years ago.
“Our district is in a tremendous state of grief and sorrow,” said Robert Runcie, superintendent of the school district in Parkland, about an hour’s drive north of Miami. “It is a horrible day for us.”
Volatile
Authorities offered no immediate details about Mr Cruz or his possible motive, except to say that he had been kicked out of the high school, which has about 3,000 students. Students who knew him described a volatile teenager whose strange behaviour had caused others to end friendships with him.
The suspect was found by police at the nearby town Coral Springs. He was taken into custody and transferred to a nearby hospital, before being moved to a police station.
Of the 17 victims, 12 died in the school, and two just outside the building, the sheriff said. Two further victims died in the hospital, while one person was shot on the street. The victims were both pupils and teachers.
The suspect “was taken into custody about an hour after he left Stoneman Douglas after he committed this horrific, detestable act,” the sheriff said. He urged the public to be aware of any signs of violence or disturbing pictures on social media. “If you see something, say something,” he said.
An AR-15 style firearm has been seized by police, and the Bureau of Alcohol, Tobacco, Firearms and Explosives is believed to be currently tracing the firearm.
Mr Runcie said police had received “no warnings, no threats,” about an imminent attack. “It’s a day that you pray, every day, that we will never have to see. I ask the community for their prayers, their support for these children and their families. We are going to do whatever we can to come together as a community to come through this.”
Shortly after the attack, Mr Trump and department of homeland security secretary Kirstjen Nielsen spoke by phone to Florida’s governor Rick Scott and to various state and local officials. The president offered federal assistance to the governor, the White House said.
US vice-president Mike Pence said: “Our hearts break for all the victims and families affected by today’s terrible school shooting in Broward County, FL. These students, teachers, administrators, and families will all remain in our prayers,” he said.
Wednesday’s attack, which took place on St Valentine’s Day, is the fourth fatal gun incident to take place at an American school in 2018. Last month a student at a Kentucky high school shot 16 people, killing two other 15-year-olds. – Additional reporting: PA