Authorities say two suspects are in custody following a shooting at a suburban Denverschool that injured at least seven students.
Fox News says that classrooms are being cleared at the school one by one.
It's possible that a third suspect remains in STEM School Highlands Ranch, which is still being searched, Douglas County Undersheriff Holly Nicholson-Kluth said at a news conference.
Authorities are now engaging a third suspect, the source said.
Authorities said over Twitter that they responded to a "call of shots fired" at STEM Schools Highlands Ranch at 1:53 p.m.
Nicholson-Kluth said authorities don't know at this point if the suspected shooters were students. At the time of this article, police consider the scene "active" and "unstable".
Parents were instructed to pick up their children nearby at the Northridge Recreation Center.
The STEM school has been placed in lockdown.
The school was surrounded by first responders, Kelly said.
Colorado Gov. Jared Polis said the state is making all public safety resources available to assist the sheriff's office. "We will provide more information as soon as we have it", according to Douglas County School District.