Watch: 'I saw two girls probably dead in the hallway' - student's chilling account of chaos during Florida school massacre

A horrifying account of the carnage inside the Florida high school in which 17 people were killed today, has been provided by a student who describes running with classmates through bloody hallways to escape the violence.

Speaking outside Florida's Marjory Stoneman Douglas High School following the attack, a female teenage student recounts rushing through the school, not knowing which way to safely shelter.

"We were in the classrooms on the third flood, we ran to the staircase, but then everyone paused and we all started running back," the student said told Fox News.

"I was being pushed and pulled through the hallway, and we ran to the classroom and the minute I got into my classroom I heard gunshots, multiple rounds.

"I'm not sure from what gun, we were in there for, I don't even remember, a really long time and then the police came through the hallway to get us.

"In the hallway I saw a big pile of blood like kind of smeared as if they were dragged away, and I saw two girls probably dead in the hallway.

"Then coming down the stairs there was some more blood, and then coming out the building there was another guy, it was probably a teacher who I'm pretty sure was dead outside."

Seventeen students and teachers are dead and at least 14 have been taken to hospital, with three in critical condition, after today's mass shooting.

It's the second worst in US school history, eclipsing the infamous Columbine shooting, which left 15 dead including the two shooters in 1999.

The sole suspect in the attack is 19-year-old Nicolas Cruz who was expelled Florida's Marjory Stoneman Douglas High School.

He has been described by past classmates as having a fixation on firearms and and often carrying "multiple guns" and showing them to other students.

The suspected shooter Cruz was found off campus this morning (NZT), with reports he blended into fleeing students to escape to a nearby suburb where he was captured by police.

Cruz was checked out at a hospital after his arrest and is now being held at a secure location in a public building.