A shooting at a high school in the US state of Colorado left three students critically injured, according to local authorities.

The Jefferson County Sheriff’s Office said the incident took place at Evergreen High School shortly after midday on Wednesday.

The victims, all students, were transported to St. Anthony Hospital, where they remain in critical condition, ABC News reported.

Local police confirmed that the suspect was "neutralised" at the scene.

Officials did not immediately provide further details about the identity of the shooter or whether the person was killed.

The school was placed on lockdown as officers continued to secure the campus and search for any additional threats.

"FBI Denver is aware of the situation in Evergreen, Colo. We have personnel responding and stand ready to assist," the agency said in a post on X.

Parents were told to gather at a designated reunification site to await updates from law enforcement.

Helicopter footage broadcast by local outlets showed dozens of emergency vehicles surrounding the school and heavily armed officers entering the building.

Colorado has a history of deadly school shootings, including the 1999 Columbine High School massacre in Jefferson County, which killed 13 people, and the 2012 Aurora movie theater shooting.

Both incidents helped galvanise debate in the United States over gun laws, school safety and mental health resources.

Wednesday’s shooting once again reignited fears among parents and students about campus security, coming amid a year of heightened concern over gun violence in schools nationwide.