The shooting began in the middle school and that many shots were fired, according to the Sheriff's Office.
At least seven people were injured during a Tuesday afternoon shooting at a charter school in Colorado's Douglas County south of Denver. "ABC News reports "multiple people shot", with two suspects in custody, police "engaging a third".
Some students remained in the school and authorities are now working to evacuate the elementary school, Nicholson-Kluth said.
The situation was considered "still active and unstable" with deputies identifying and locating those involved the Douglas County Sheriff's Office said on Twitter.
The STEM school elementary school students were being held in the elementary gymnasium as of 3 p.m.
The sheriff directed parents to a recreational center to pick up their children.
A first responder helicopter lifts off near STEM School Highlands Ranch.
The Denver office of the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) also tweeted that they were responding.
The STEM school is on lockdown, and all other Douglas County schools are on lockout, the network added.
Additional information was not immediately available. "The heart of all Colorado is with the victims & their families", Polis said.