Officials say eight students have been injured in a shooting at a public charter school in Highlands Ranch, Colo., a suburb south of Denver.

Two suspects are currently in custody. Douglas County Sheriff Tony Spurlock said one suspect is an adult male and the other is a juvenile male. Both are students at STEM School. Spurlock said their names are being withheld pending further investigation. The suspects were not previously known to local law enforcement.

"This is a terrible event. This is something that no one wants to have happen in their community," Spurlock said in a press conference late Tuesday afternoon. "Two individuals walked into the STEM school, got deep inside the school and engaged students in two separate locations."

"We do have eight students in area hospitals right now. Several of them are in critical condition," he added.

All of the victims are 15 years and older.

The STEM School has 1,800 students in kindergarten through 12th grade.

Authorities saidover Twitter that they responded to a "call of shots fired" at STEM Schools Highlands Ranch at 1:53 p.m. MT. They initially described the situation as unstable and were directing parents to pick up their children at a nearby staging area.

Spurlock said the first officers reached the school two minutes after receiving reports of shots fired at the school. He said he believed their quick response "saved lives."

He offered no information on any possible motivation for the attack nor the suspects' methodology. A handgun was recovered, but Spurlock released no other information about weapons.

The FBI is processing the crime scene. Investigators from Alcohol, Tobacco and Firearms (ATF) and the Department of Homeland Security are also assisting the investigation.

Earlier, the Douglas County School District announcedall schools are on lock down and have canceled all after school activities.

White House spokesman Judd Deere released the following statement on the shooting: "Our prayers are with the victims, family members, and all those affected by today's shooting at STEM School Highlands Ranch in Littleton, Colorado. Tragically, this community and those surrounding it know all too well these hateful and horrible acts of violence. The White House has been in communication with state and local officials, and the President has been briefed and continues to monitor the ongoing situation. We offer our full support to local law enforcement and first responders and thank them for their heroism."

This is a developing story. Details may change as more information becomes available.