A Fort Jackson trainee is in custody after allegedly hijacking a South Carolina elementary school bus with 18 children on board while carrying a rifle, authorities said.

The Forest Lake Elementary students and the bus driver are safe, Richland County Sheriff Lott said at a news conference.

The 23-year-old trainee’s weapon did not have ammunition, Fort Jackson Commander Brig. Gen. Milford H. Beagle Jr. said at a news conference, adding that the children and driver could not have known that.

Lott called this “one of the scariest calls that we could get in law enforcement.”

The incident began around 7 a.m. Thursday when the suspect allegedly hopped a barbed wire fence and fled Fort Jackson, according to Lott and Beagle.

The children had boarded the bus when the armed suspect, Jovan Collazo, got on and allegedly “told the bus driver he didn’t want to hurt him, but he wanted him to drive him to the next town,” Lott said.

The sheriff’s office released surveillance video from inside the school bus showing the suspect pointing a rifle at the bus driver and telling him to drive.

The bus driver started driving and Collazo brought the children to the front of the bus, Lott said.

“The kids started asking lots of questions to the suspect if he was going to hurt them or the bus driver,” Lott said.

“The suspect got a little frustrated,” Lott said, and the driver pulled over.

After six minutes on board with Collazo, the children and the bus driver got off safely, Lott said.

The suspect then drove the bus for a few miles before abandoning it, leaving the rifle inside, Lott said.

Collazo was spotted by deputies and civilians and was arrested without incident, Lott said. He faces charges including kidnapping, Lott said.

Beagle described the trainee, believed to be in his third week at Fort Jackson, as a quiet 23-year-old from New Jersey. He said it appeared the trainee was trying to get home.

“There is nothing that leads us to believe in his counseling, in his screening records coming in, that this had anything to do with harming others, harming himself or anything that links to any type of nefarious activity,” Beagle said. “We do experience several soldiers that over the course of initial stages have that desire, that anxiety, and due to separation from their families, to get home. We think that was truly his intent and nothing beyond that.”

Fort Jackson officials issued an apology, saying in a statement, “This was a failure in our accountability procedures that we truly regret and are apologetic to our community.”

Richland County School Board Chairman James Manning said, “I’ve been on the board now for over 10 years and I have never received a call that scared me as much as the call that I received this morning — that a bus had been hijacked with our students and staff.”

The students were taken to school “where they received support from school employees and counselors and were reunited with their parents/guardians,” the school district said.

Superintendent Baron Davis said in a statement, “Once we were certain all students were accounted for and physically safe, we immediately began deploying social and emotional counseling resources to the school so that our students could begin the process of healing as they are dealing with a traumatic event. We will continue to provide counseling services for the students and their families, our bus driver and employees as long as necessary.”

Lott praised the bus driver who he said “kept his cool” and “kept the situation calm.”

“His main concern was the safety of those kids and he did his job,” Lott said.

ABC News’ Luis Martinez contributed to this report.