"They were chasing someone around the corner because I heard it, this corner, that corner, that corner then all of a sudden they ended up there about a block away and then all of the sudden from there I heard a bunch of gunshots go off," neighbor Codey Sias told CBS-TV, Denver.
The injured officer was transported from the intersection of 34th Avenue and Mariposa Street to Denver Health Medical Center at about 3:30 p.m., the TV station said.
His injuries were described as serious but not life-threatening.
Four suspects have been identified in the incident, and police were searching for a fifth suspect.
One suspect was shot and killed at the scene. Another suspect who was attacked by a K-9 officer was rushed to a hospital with serious injuries. A female suspect was being treated at a hospital for injuries "consistent with a car crash," the TV station said, while a fourth suspect was in critical condition with gunshot wounds.
Lockdowns were ordered at Horace Mann Elementary School, Trevista Elementary at Horace Mann, Bryant Webster Dual Language School and Sandoval Elementary School. Parents were told they could not pick their children up until police lift the lockdown.