By Annie Gimbel | CBS 11 News

SOUTH FLORIDA (CBSDFW.COM) – Reports of an active shooter inside a Florida high school started hitting airwaves Wednesday afternoon as one student inside the building took to Twitter to document the terror.

Twitter user @TheCaptainAidan (who says he’s a freshman) shared the following:

Ambulances converged on the scene atMarjory Stoneman Douglas High School in Parkland, Florida as emergency workers appeared to treat possibly wounded people on the sidewalks. Despite news footage showing many students safely exiting the school, many parents said their children were still hiding inside.

Students like “Aidan.”

One parent, Cesar Figueroa, told CBS News his daughter is in the school hiding in a closet with a friend and is too petrified to talk. Figueroa said waiting to hear from her via text was the longest 20 minutes of his life.

He said she heard shots fire, saw a window blown out — screamed and ran into a closet with friends.

At fifteen till 3 p.m., the student tweeted about the overwhelming response he was receiving.

Television news cameras showed a young man with reddish hair wearing a red shirt who was surrounded by SWAT officers and put in handcuffs and being taken into custody by 3 p.m.

Not long afterward, the student tweeted the following shortly before 3:30 p.m.

“It’s a horrific situation,” Broward County Superintendent Robert Runcie said. “It’s just a horrible day for us.”

President Trump tweeted: “My prayers and condolences to the families of the victims of the terrible Florida shooting. No child, teacher or anyone else should ever feel unsafe in an American school.”

Deputy White House Press Secretary Lindsay Walters said, “We are monitoring the situation,” she said. “Our thoughts and prayers are with those affected.”

Another student later shared this video of SWAT evacuating his classroom.

(© Copyright 2018 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)