PARKLAND, Fla. – Seventeen people were killed and more than a dozen others were taken to area hospitals after a shooting Wednesday at Marjory Stoneman Douglas High School in Parkland, Broward County Sheriff Scott Israel said.

The lone shooter was taken into custody off campus without incident.

Israel told reporters that Nikolas Cruz, 19, was previously expelled from the high school.

Israel said Cruz used an AR-15 rifle in the shooting and was equipped with multiple magazines. The sheriff said 12 people were found dead inside the school, two just outside the building and one on Pine Island Road. Israel said two other victims died at the hospital.

Dr. Evan Boyar, medical director of Broward Health North's Department of Emergency Medicine, said 17 patients were taken to area hospitals, including nine to Broward Health North, seven to Broward Health Medical Center and one to Broward Health Coral Springs.

He said the suspect was among those treated at Broward Health North before he was released back to police.

Authorities and school officials did not immediately say why Cruz had been expelled from the school, but a student who had a class with him last year told Local 10 News that he got into trouble after bringing a weapon on campus.

"I heard that he wasn't allowed to bring a backpack to school because they found a weapon in there, so ever since that day, he would bring a plastic bag," she said.

The teen said she told her parents last year that she was afraid of Cruz and that he would tell his peers that he wanted to join the military so he could shoot people.

Cruz was seen walking into the BSO's headquarters in a hospital gown hours after the shooting, where he would be questioned by detectives before being taken to jail.

Two law enforcement officials and a witness said Cruz was able to leave the school after the shooting by blending in with other students who were trying to escape.

Broward Sheriff's Office spokeswoman Keyla Concepcion said deputies were initially called to an active shooter at the school shortly before 3 p.m.

A view from Sky 10 showed the SWAT team converging on the school with their guns drawn.

At least two people were seen on stretchers. One of them was placed into the back of the ambulance.

Rescuers appeared to have a triage unit set up under a tent outside the school.

Students could be seen being guided off campus. Some of them had their hands in the air and others were walking out with their hands on each other's shoulders in a human chain.

It appeared that students were dropping their backpacks in the middle of the street as they were being guided to safety. A crowd of students could be seen sitting on the grass next to the road.

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"I was in the building right in front of the shooter -- right where he pulled the firearm," ninth-grade student Dominic Timpone said. "Me and my friends were going downstairs because we thought it was a firearm, and he was loading up the gun and we ran upstairs and said, 'Everyone get into the classroom.'

"We hear bullets coming closer and closer to us, and then we just hear kids screaming. This teacher was apparently trying to help a student and got shot."

A parent of a ninth-grade student told Local 10 that she was speaking to her daughter via text message.

"She's telling me that she is OK," the woman said. "The teacher has them in the back of the classroom. He locked the door. They know what to do. They're doing the proper procedure, but she's terrified."

The woman said her daughter heard at least one gunshot.

"I'll be relieved when she comes out and I can give her a hug," she said.

Parents who spoke to Local 10 News expressed various feelings about the shooting, ranging from sadness to anger.

"I'm so angry," a woman who was waiting to find her son said. "How many times does this have to happen?"

A junior at the school told Local 10 he heard the shots and took off running.

"This is a terrible day for Parkland, Broward County, the state of Florida and the United States," Israel said. "My very own triplets went to that school and graduated from Stoneman Douglas. They played football and lacrosse at that school, so it's just catastrophic. There really are no words."

Israel said the shooter "was outside and inside at varying times."

Deputies and Coral Springs police on Twitter were asking parents to pick up their students at the Marriott on Heron Bay Boulevard.

Parents of children who attend nearby Westglades Middle School were able to pick up their children shortly before 6 p.m. at the school. Pine Island Road remained blocked, but parents could enter from Coral Ridge Drive via Holmberg Road.

Authorities cleared out the high school hours after the shooting.

"It's one of the biggest schools in Broward County. It's huge. It's a huge campus, so we have multiple SWAT teams clearing every building to make sure that there are no other shooters," Israel said before the scene was cleared.

Gov. Rick Scott and Israel addressed reporters at news conference just after 9 p.m.

“How could this happen in this state? This a state that is focused on keeping all of our children safe. You come to the conclusion that this is absolutely poor evil,” Scott said. "My prayers are with everybody impacted."

Florida Attorney General Pam Bondi said the state would pay for funeral expenses. The school system said it will offer counseling services for the students, teachers and parents.

Israel said he also spoke to President Donald Trump, who "offered the full power of the United States of America to help us get through this."

The shooting was the 19th at a U.S. school so far in 2018.

Marjory Stoneman Douglas High School will remain closed through Friday. All school activities are also canceled for the week. School officials said Westglades Middle School will be open for the rest of the week, but grief counselors will be at the school for students and staff as needed.

The FBI has established a tipline following the shooting. Anyone with information about the Parkland school massacre is asked to call 1-800-Call-FBI.