Swanson Elementary School in Arvada, Colo., near Denver was evacuated Wednesday after a suspicious backpack was discovered.
According to CBS Denver, officials allowed students and staff back into the facility.
Police said the evacuation was issued due to a threat.
The Denver Channel reported that Arvada Police spokeswoman Jill McGranahan are inspecting a backpack that might have chemicals in it.
Students were evacuated and are in an area outside the school.