At least 17 people have been killed in a mass shooting at a high school in Parkland, Florida, police say.
The suspect has been named as Nikolaus Cruz, 19, and is a former student at the school who had been expelled.
Cruz, who was armed with "multiple magazines", began the shooting spree outside the school before opening fire inside, according to officials.
It is one of the deadliest school shootings since 20 children were killed at a Connecticut school in 2012.
Broward County Sheriff Scott Israel told reporters that Cruz had used a rifle and opened fire outside the school where three people were killed. He then entered the building and killed 12 people.
Two people later died after being taken to hospital.
"It's catastrophic.There really are no words," Sheriff Israel tweeted later.
Dr Evan Boyar of Broward Health told reporters late on Wednesday that 17 people had been taken to area hospitals.
He added Cruz was among those treated and was released into police custody. Three people remained in a critical condition and three others were in stable condition, he said.
How it unfolded
Earlier on Wednesday, the local public school district tweeted that "students and staff heard what sounded like gunfire" shortly before dismissal at the Marjory Stoneman Douglas High School.
Police and SWAT team members began clearing students from the high school in Parkland, about an hour north of Miami, as parents and ambulances gathered outside.
Cruz was taken into custody without incident about an hour after he left the high school, according to police.
Several witnesses inside the building at the time told news outlets that the fire alarm had been set off as the shooting began.
Students told US media they hid under desks, in closets or barricaded doors as loud shots rang out, reports BBC.