Police in Florida have arrested a suspect after they were called to a major shooting incident at a local high school.
More than an hour after the shooting began, the Broward Sherriff's Office said the "shooter is now in custody."
It is not yet clear how many people have been killed or injured.
But it warned that the scene at Stoneman Douglas High School in Parklands "is still active".
School superintendent Robert Runcie told reporters: "There are fatalities involved here."
He also said the suspect was "potentially a former student… that individual, we believe, is in custody."
"So far we have at least 14 victims," the Sherriff's department said, without specifying their condition.
US media outlets reported that up to 20 people may have been injured, while some have been evacuated.
A local Fox news worker reported seeing several people being treated for injuries outside the school.
The local public school district tweeted: "Today, close to Marjory Stoneman Douglas High School's dismissal, students and staff heard what sounded like gunfire."
"The school immediately went on lockdown but is now dismissing students. We are receiving reports of possible multiple injuries," it said.
Video footage from the scene showed students being evacuated in small groups, while armed police patrolled the school's perimeter.
Coral Springs Police department, meanwhile, tweeted instructions to teachers and students to "remain barricaded inside until police reach you".
The FBI also said it was attending the scene and assisting local law enforcement.
US television networks reported large numbers of parents had gathered outside the police perimeter.
President Donald Trump tweeted condolences "to the families of the victims". White House Deputy Press Secretary Lindsay Walters said the president had been briefed and that the White House was monitoring the situation.