Seventeen people were killed Wednesday (Feb 14) when a 19-year-old former student opened fire with a semi-automatic rifle at a Florida high school, the local sheriff said, calling the scene "horrific".
Broward County Sheriff Steve Israel said the victims were a mix of students and adults, though he could not confirm if the adults were teachers. Twelve of the victims had been inside the building, he added.
He identified the suspect as Nikolas Cruz, a former student at the Marjory Stoneman Douglas High School who had been expelled for "disciplinary reasons."
Cruz was arrested without incident in the nearby town of Coral Springs after the Valentine's Day rampage and taken to hospital with minor injuries, the sheriff said.
"We have already begun to dissect his websites and things on social media that he was on and some of the things ... are very, very disturbing," Israel said.
"He had countless magazines, multiple magazines, and at this point, we believe he had one AR-15 rifle," the sheriff added.
Israel said he was uncertain about the exact number of people injured, but at least 14 were taken to hospital and two had died there of their wounds.
The shooting, one of several in the United States since the start of the year, will once again throw the spotlight on the country's epidemic of gun violence and the ready accessibility of weapons, with 33,000 gun-related deaths annually.
"This is a terrible day for Parkland," Israel said, speaking of the city of about 30,000 people, located 50 miles (80 kilometres) north of Miami.
"My very own triplets went to that school."
A teacher at the school told the Miami Herald that Cruz had been identified previously as a potential threat to his classmates.
"We were told last year that he wasn't allowed on campus with a backpack on him," math teacher Jim Gard said. "There were problems with him last year threatening students, and I guess he was asked to leave campus."
A law enforcement source told CBS News that the gunman pulled a fire alarm before opening fire, but Israel said he could not confirm that report.
"Just a horrible day for us," Robert Runcie, the superintendent of the county's school district said, adding that the incident appeared to be over.
"This is a very tragic situation for everybody involved," Parkland Mayor Christine Hunschofsky told CNN, adding that she had spoken to a number of students.
"They were very scared," she said. "And almost in shock when they came out."
Asked about security, the mayor said a police officer is always stationed at the school and there was a "single point of entry."
Television images showed students being led out of the school by heavily-armed police officers and an armoured vehicle filled with a SWAT team arriving at the scene.
One injured victim was seen being placed into an ambulance on a stretcher.
Police officers in helmets, bulletproof vests and armed with automatic weapons could be seen stationed at several points around the sprawling school complex, which houses nearly 3,000 students.
'EVERYONE STARTED RUNNING'
Student Jeiella Dodoo told CBS News that she and her schoolmates had evacuated their classroom calmly after hearing what they thought had been a routine fire alarm.
"The alarm went off so we had to evacuate from our classes," she said. "Then we heard gunshots.
"I heard about six gunshots," she said, "and then some people started running and then everyone started running because we were like 'If it's real, then just run.'"
A math teacher at the school told CBS that he was hiding with six of his students. "We are fine. We are waiting," he said.
Caesar Figueroa told CNN his daughter was hiding in a closet and texting her family.
"She's trapped with her 10 friends. She said she heard gunshots. A window blew and everybody is screaming and running, and she said she ran in the closet and she's still there," Figueroa said.
NO CHILD SHOULD 'FEEL UNSAFE'
"My prayers and condolences to the families of the victims of the terrible Florida shooting," President Donald Trump said on Twitter.
"No child, teacher or anyone else should ever feel unsafe in an American school."
Since January 2013, "there have been at least 283 school shootings across the country - which averages out to one school shooting a week," according to Everytown for Gun Safety, a non-profit group that advocates for gun control.
Since the 2012 massacre at the Sandy Hook Elementary School in Newtown, Connecticut, where 20 children and six adults were shot dead, warning procedures and emergency drills have multiplied at US schools.
The goal is to teach school children how to react to a shooter who opens fire at random.