One student is said to be in a critical condition following a shooting at a Colorado School.

Police in the US state responded to a reporting shooting at Arapahoe High school in Denver this afternoon.

Two students have been injured, one of them is in a critical condition according to a spokesperson from a local hospital.

Local county Sheriff Grayson Robinson gave a news conference on the unfolding events.

He reported: "12.33 this afternoon, an individual came to the Arapahoe High School on the West Side and entered the school armed with a shotgun. Was looking for an individual teacher that he identified by name.

"The teacher began to understand that he was being looked at. Exited the school. One student confronted the armed student and was shot. That student has been transported in a serious condition to a local hospital. We immediately activated our active shooter protocols.

"We have resources from the South metro area assisting us. We cleared the school an secured all of the students very quickly. While we were clearing the school we found one additional student with a minor gunshot wound. That student has also bee transported to a local hospital.

"While we were securing the school and ensuring the safety of the students and the teachers in the school we located what we people to be the suspect and the active shooter. That individual is deceased and he apparently killed himself. That will still be part of the investigation.

"We know the identity of the suspect. I am not going to release it at this time. I want to repeat to you that the suspect has been found inside the school and he has deceased as a result of what appears to be a self-inflected gunshot wound.

"We are slowly and methodically clearing the school and ensuring that all of our students are safe. They were safer in their locked school room classes than they would have been had we allowed them to exit. We are know slowly and methodically allowing the children to leave the school in groups. We are bringing them to directly east of where we are standing.

"They will be boarded on buses and transported to a church South of here called Shepherd of the Hills. It is at Shepherd of the hills that we will reunite families with the students. We have no directed all families to go to the Shepherd of the Hills Church so they can be reunited with the students in the next half hour to forty-five minutes.

"I will also tell you that the response protocols around active shooters were put into place immediately. The first deputy sheriffs and police officers that were on scene immediately entered the school to engage the shooter if they could locate that individual."

The school and others in the area have been placed on lockdown. Children were seen being lead out of the school in single file with their arms raised.

The surburban school is said to have over 2,200 students and 70 classrooms.

Arapahoe High School is 8 miles east of Columbine High School where in 1989 two teenage shooters killed 12 classmates and a teacher before killing themselves.