One person died after two suspected student shooters opened fire at a STEM school in the Denver suburb of Highlands Ranch. Eight others were injured and both suspects are in custody, officials said.

The Douglas County Sheriff’s Office said it responded to the STEM School Highlands Ranch just before 2 p.m. Tuesday when a school administrator called dispatch to report shots fired. Authorities believe the suspects used a handgun.

"Two individuals walked into the STEM school, got deep inside the school and engaged students in two separate locations," Douglas County Sheriff Tony Spurlock said.

The sheriff's department confirmed that one student, an 18-year-old male, was killed in the shooting. The father of Kendrick Castillo told NBC News that his son was the student killed, but the family declined to be interviewed Tuesday night.

The adult suspect was identified by the Douglas County Sheriff's Office on Tuesday night as Devon Erickson, 18.

Authorities identified a second suspect as a juvenile female, but a public defender clarified that the juvenile prefers to use male pronouns. NBC News is not identifying the underage suspect, who has not yet been charged.

Devon Erickson, a suspect in the shooting at a STEM School in Highlands Ranch, Colorado. via Facebook

Spurlock said that several of the people who were injured are in critical condition and some were in surgery. At least three of the injured have since been released from an area hospital Tuesday evening.

The shooting occurred in the middle school and officers heard shots as they were entering the school, officials said earlier in the day.

“The only thing that we know of right now from one interview is that we have a handgun. Other than that I cannot tell you of other weapons,”Spurlock said.

Authorities secured a suspect's vehicle and were seeking warrants to search the car as well as the suspects' homes.

Multiple agencies, including the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives, responded to the scene to assist.

The White House said in a statement that it was in contact with law enforcement and that President Donald Trump was monitoring the situation.

"Our prayers are with the victims, family members, and all those affected by today’s shooting at STEM School Highlands Ranch in Littleton, Colorado," the statement said. "Tragically, this community and those surrounding it know all too well these hateful and horrible acts of violence."

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Students at the public charter school for science, technology, engineering, and mathematics were being evacuated.

STEM School Highlands Ranch has 1,850 students — 550 elementary age students, 700 in middle school and 600 high school students, according to the district.

Kendrick Castillo was fatally shot at a STEM School in Highlands Ranch, Colorado. John Castillo / via Facebook

Rocco DeChalk, who lives blocks from the school, heard a stampede of students running past his house.

“I saw all of them running, so I thought it was a gym class at first,” he said. “But then I saw there were so many of them.”

After going outside, he saw a teenage boy shot in the back and sitting by a mailbox two doors down. The boy was with a teacher and a friend, who had been applying pressure to a bullet wound.

They called 911 and the dispatcher told them to take cover, so they helped the young victim into DeChalk’s kitchen. The man eventually flagged a passing policeman who then caught the attention of an ambulance, which rushed the youngster away.

All the while, the boy remained conscious.

“He made a comment, 'Oh, I’m starting to feel it now,'" DeChalk said referring to the pain. “I told him that was probably the adrenaline kicking in and he was going into shock.”

Nyki Giasolli said her daughter, Kamananui, was in the classroom when a shooting happened. Giasolli said she was told by her daughter that people came in shooting.

“She said that two of her classmates took the shooters down, and she was able to escape,” Giasolli told KUSA. "She just said there were people shot; that’s all I know.”

Her daughter, who is a senior, and her son, Kupono, a freshman, are both safe.

“She called me, and she was hysterical and she told me that there had been a shooting,” Giasolli said.

Giasolli said her daughter said the shooters were students.

“We chose a small school because we thought they’d be safer, because we thought that everybody would know everybody,” she said.

Children file out of the STEM School Highlands Ranch on Tuesday. KUSA

Another parent told KUSA that her son was apparently in a room next to where the shooting occurred and was safe with a teacher. That teacher called her to let her know her son was OK.

She said that the school has been sending automated voice messages and was told there was a lock down.

The campus is just eight miles southeast of Columbine High School in Littleton, site of the April 20, 1999, mass shooting in which two gunmen murdered 12 fellow students and a teacher before killing themselves.

The shooting comes just weeks after a Florida woman, Sol Pais, sparked a security scare that shut down area schools after authorities said she appeared to have an “infatuation” with the Columbine shooting and had purchased a shotgun in the area.

Pais, 18, was found dead on April 17, two days after she flew to the area, of an apparent suicide, authorities said.

Before this incident, two people had been killed and six injured in three school shootings in 2019, according to NBC News research.