School massacre: Terrifying video shared by student inside classroom as shots fired

WARNING, DISTRESSING CONTENT: A student locked down in his Florida classroom has captured the horrifying moment he and his classmates cowered on the floor as a gunman opened fire at the school.

At least 17 people have been killed after a gunman stormed the Marjory Stoneman Douglas High School in Parkland, 72km north of Miami, at the end of the school day on Wednesday.

In the confronting footage shared to Twitter, students hiding on the ground can be heard screaming as the shots echo through the classroom.

“Our f****** school is getting shot up,” the caption reads.

Students terrified screams echoed through the room as gunshots continued to ring out. Source: Twitter

A second video shows bulletholes through the classroom's computers.

A federal official has identified the Florida school shooting suspect as Nicolas Cruz, a former student at the school.

Twelve of the dead were killed inside the school building, two others just outside, one more on the street and two other victims died of their injuries at a hospital, Broward County Sheriff Scott Israel said.

He said the victims comprised a mixture of students and adults.

A woman is rushed from the school by paramedics. Source: Getty

"There was a time when he did attend the school," Israel said.

"I don't know why he left, I don't know when he left."

It was the 18th shooting in a US school so far this year, according to gun control group Everytown for Gun Safety.