Update (4:00 PM EST):
Arapahoe County Sheriff Grayson Robinson reports the alleged shooter has died of a self-inflicted wound.
One student is said to be in critical condition due to gunshot wounds.
Arapahoe High School in the Denver, Colorado metropolitan area is reportedly on lock-down after shots were fired Friday afternoon, Arapahoe County Sheriff Grayson Robinson told Call 7.
Robinson said that at least two people are injured, their conditions unknown, and the shooter is believed to still be in the school.
The school is attended by 2,200 students and is located in Centennial, Colorado—8 miles from Columbine High School where a school shooting in 1999 left 15 students, including the shooters, dead.
News and photographs are pouring in via Twitter.