Jaime Guttenberg is the first person to have been confirmed dead from the horrific Florida school shooting.

The teenager attended Marjory Stoneman Douglas High School with her brother Jesse. He made it home safely.

Jaime's photo was among the dozens of pictures parents shared on Facebook, hoping someone from the school community would have information about their children.

In this frame grab from video provided by WPLG-TV, law enforcement personnel arrest an unidentified man (in dark red), following the shooting. Photo / AP
In this frame grab from video provided by WPLG-TV, law enforcement personnel arrest an unidentified man (in dark red), following the shooting. Photo / AP

Close to 3000 Facebook users shared Jaime's picture before the post was removed.

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It's believed the post was removed after her parents, Fred and Jennifer Guttenberg, learned she had died.

Jaime's father previously posted a status on Facebook, appealing for information and posting his phone number.

"For those wondering, I have Jesse and he is OK. We cannot reach Jaime. If anyone has a child who saw or spoke to Jaime, please call me at ..."

Friends of Jaime's have begun posting tributes for the teenager on Facebook, calling her a "special loving and charismatic young lady".

The Broward Sheriff's Office is yet to release the identities of the other people who have died.

Ben Wikander, another teenager who attended the school where 17 people were shot dead, was among the 16 people rushed to hospital.

His parents hadn't heard from him all afternoon and decided to use Find My iPhone which led them to a local hospital.

Hours later, Ben's father found out he had been shot three times and was undergoing emergency surgery at Broward North.

Parents meet at a hotel in Coral Springs, Florida, to pick up their children, following a shooting at nearby Marjory Stoneman Douglas High. Photo / AP
Parents meet at a hotel in Coral Springs, Florida, to pick up their children, following a shooting at nearby Marjory Stoneman Douglas High. Photo / AP
Waiting for word from students anxious family members gather at Coral Springs Drive. Photo / AP
Waiting for word from students anxious family members gather at Coral Springs Drive. Photo / AP

Earlier, a teenager caught up in the horrific Florida school shooting has revealed how a teacher lost his life trying to save his students.

The student, named as Alex, told South Florida News WSVN7, she was inside a class when the gunman walked past.

She and others hid in a room her teacher had unlocked for them.

But he was shot by the gunman and died as he tried to lock the students safely inside.

"So we heard our fire alarm for the second time that day which is weird," she said

"We all got upstairs and into the classroom, and when he tried to unlock the door, me and a couple other people ran in, and as he was closing the door, he was actually shot and killed right there."

Students released from a lockdown walk away following the shooting. Photo / AP
Students released from a lockdown walk away following the shooting. Photo / AP

She said the door was left open the whole time and the gunman could have walked in but students tried to hide or lie on the floor so the gunman wouldn't notice.

Alex's mother said it made her sick to realise the teacher was killed.

"He was trying to lock the door and keep them safe and was shot," she told the broadcaster.

The family had only moved to Florida from Canada a few months ago.

"The thought this would be where we would be with a school shooting is just a nightmare," she said.

Alex was one of hundreds of students caught inside the Marjory Stoneman Douglas High School in Parkland when the horror unfolded.

Florida police say suspect Nikolas Cruz, 19, entered the school grounds and opened fire, leaving at least 17 people dead.

It comes as police revealed the shooter, who was previously a student at the school, was identified as a potential threat to students previously.

Student Daniel Huerfano told The Associated Press he remembers seeing Cruz walking around the school with his lunch bag, adding, "He was that weird kid that you see ... like a loner."

Meanwhile Florida Senator Bill Nelson of Florida said shooter wore a gas mask and had smoke grenades.

The Florida Democrat said in an interview with CNN that he was briefed on the attack by the FBI.

Sen Nelson said the attacker "set off the fire alarm so the kids would come pouring out of the classrooms into the hall. And there the carnage began."

He said he did not know if the gunman had used the smoke grenades but assumed that's why he had a gas mask on.

Maths teacher Jim Gard told the Miami Herald he though the second fire drill was strange.

"Six kids ran back into my room, and I locked the door, turned out the lights and had the kids go to the back of the room," he said.

"I told the kids to hang in there, it may still be a drill."