Two people have been injured in a shooting at a high school near Denver, Colorado, US media report.
Police have said there is an "active shooter situation" inside Arapahoe High School in Centennial, Colorado.
The school and others in the area have been placed on lockdown.
The shooting was reported the day before the anniversary of the shooting in Newtown, Connecticut, in which 20 schoolchildren and six workers were killed at a primary school.
Students could be seen on television footage streaming out of the school in single-file lines with their hands above their heads.
The school is said to have more than 2,200 students and 70 classrooms.
The building is just eight miles (13km) east of Columbine High School in Littleton, Colorado, the site of a mass school shooting in April 1999 which left 14 students dead.
Get rid of the guns 
My school went on lock down 
