Jason Dunkel, spokesman for Littleton Adventist Hospital, says the student was in surgery Friday. It's unclear how the student was wounded.
Colorado division of emergency management spokeswoman Micki Trost said her director went to Arapahoe High School in Centennial after reports of an active shooter. There weren't any more immediate details.
Police were outside the school, and students were seen walking toward the school's running track with their hands in the air. Television footage showed students being patted down.
The school is about 8 miles east of Columbine High School in Littleton, where two teenage shooters killed 12 classmates and a teacher before killing themselves in 1999.