A ranking law enforcement source told Scripps affiliate KMGH-TV that at least one victim was shot and that one suspect was down.
Initial reports indicate that two suspects are in custody, and that "multiple" students are hurt.
The sheriff confirmed seven student injuries, possibly eight, and two suspects are in custody. No information was given to an age range of the victims and how numerous victims could be children.
The reports of shots fired came at 1:53 p.m., according to a Douglas County Sheriff's Office tweet. The injured have been transported to area hospitals, Nicholson-Kluth said. Parents of students at the STEM School have been told to go to the Northridge Rec Center to pick up their child.
The school was surrounded by first responders, Kelly said.
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She said she did not believe there were any other gunmen, but tactical teams were still searching the school room by room.
Paulson's son, Christian, said he was in study hall at the school when he saw "a bunch of kids running out and saying 'School shooter, school shooter!'"
This is a breaking story and will be updated as more information becomes available.