The gunman has been taken into custody after shooting at Stoneman Douglas High School in Florida.
A math teacher caught up in the Florida high school shooting has been hailed a hero for her brave actions which helped save the lives of her students.
Mrs Shanthi Viswanathan, known as "Mrs V" to her pupils, realised something was wrong when a second fire alarm of the day rang out around Marjory Stoneman Douglas High School on Wednesday.
Instead of letting her pupils out of her Algebra lesson, Mrs V made pupils crouch on the floor in the corner of the room and put paper over the window so no one could see in.
Mrs Shanthi Viswanathan, known as 'Mrs V' to her pupils, has been praised for her quick-thinking which could have helped save her student's lives. Photo / Stoneman Douglas High School
The mother of one of her students, called Brian, claimed her quick-thinking helped save the lives of her students.
Dawn Jarboe said: "She was quick on her feet. She used her knowledge. She saved a lot of kids."
Even a SWAT team was unable to convince Mrs V of opening up the door, as she was questioned if it might have been a ploy by the gunman to gain access to the room.
Jarboe added: "She said, 'Knock it down or open it with a key. I'm not opening the door.'"
SWAT teams then smashed through the window to gain entry to the room, according to a text sent by Brian to his mother, the Orlando Sentinel reported.
In an old tribute to Mrs V, on the website Rate My teacher, she is described as a "wonderful teacher who allowed me to expand my learning platform".
It continued: "She taught me with an appreciation of math in the real world. She cares about students and often stays after school to help her students with review sessions.
"She never spends a day without teaching and always reassures every student understands the lesson. She wants every student to succeed and always tries the hardest to make sure we all do well."
Nikolas Cruz, left, with public defender Melisa McNeille, making an appearance before Judge Kim Theresa Mollica in Broward County Court. Photo / Susan Stocker
Mrs V's remarkable tale of heroism is just one of a number of stories to have emerged from the horror of the Florida shooting.
After hearing seven shots, 17-year-old student Colton Haab used his Reserve Officers' Training Corps skills to ensure the loss of life stayed at a minimum.
When he had managed to get the student from Marjory Stoneman Douglas High School into a Junior Reserve Officers' Training Corps (JROTC) room, he realised the Kevlar sheets used in the marksmanship program could be put to good use.
Recalling the fateful event, Haab said his first thoughts were: 'Where is my brother? What's going on and how do I get as many people as safe as possible as quickly as possible?'
He said: "We took those sheets, and we put them in front of everybody so they weren't seen, because they were behind a solid object and the Kevlar would slow the bullet down.
"I didn't think it was going to stop it, but it would definitely slow it down to make it from a catastrophic to a lifesaving thing."
Another student who has been hailed a hero lost his life in the attack. Peter Wang, 15, held the door open for classmates as they fled the gunman before he was killed.
Peter's grieving cousin Aaron Chan was also in the school at the time and saw him holding the door for classmates, dressed in his grey ROTC uniform.
Students from Marjory Stoneman Douglas High School evacuate the school. Photo / WPLG-TV
He carried on running and it was the last time he saw him alive.
Three heroic staff members also died while shielding their terrified students from bullets.
The three adults have been named as Scott Beigel, 35, Aaron Feiss, 37, and Chris Hixon, 49.
Beigel, a geography teacher, was shot dead as he tried to lock the door of his classroom after letting a group of fleeing students in to hide from gunman Nikolas Cruz.
Football coach Aaron Feiss threw himself on top of students, acting as a human shield, as Cruz fired his AR-15 at them.
Since Wednesday's attack, horrifying footage has emerged of bodies lying in pools of blood as hysterical students cower nearby after the Florida high school gunman stormed in and opened fire.
The disturbing videos and images were taken by students inside when suspected gunman Nikolas Cruz shot dead 17 people.
Images taken from one student's cellphone video show a girl's lifeless body lying in the middle of a classroom in a pool of blood.
Police can be seen carrying a different female student from the classroom as a number of terrified, sobbing students follow the officer cautiously to safety.
The students were forced to run through the blood-streaked halls to get outside the building, passing by several other lifeless bodies and discarded backpacks.
An official GoFundMe account has been set up to raise money to "provide relief and financial support to the victims and families of the horrific shooting".
