About an hour later, officers who remained in the area investigating the shooting "heard an excessive amount of gunfire" coming from a nearby Mobil gas station, Lundy said.
When officers got to the gas station, located near Shaw High School, they found the three victims suffering from gunshot wounds, Lundy said. The victims were taken to the hospital by police or in private vehicles, Lundy said.
Lundy said that at about 2:30 a.m., officers were called to an area of the city several blocks from the shooting scene at the Mobil gas station, where they discovered a sixth shooting victim, who was also taken to the hospital.
Lundy said no arrests connected to the shootings have been made.
A $5,000 reward is being offered for information leading to the arrest and conviction of those responsible for the shootings, Lundy said.
Police are asking anyone who was in the area of the shootings to contact the East Cleveland Detective Bureau.
The shootings prompted a response from law enforcement agencies from neighboring communities.
East Cleveland City Council President Twon Billings told ABC affiliate station WEWS in Cleveland that the Shaw High School reunion is a weekend-long event that brings together graduates and community members of all ages.
Billings said he was devastated by the shooting, and suggested that a local police shortage affected the events that transpired Monday morning.
"You have to have a presence out here," Billings said. "When you got thousands of people traveling through the city and there's no enforcement here. We only got a few officers. We had to rely on mutual aid, which you see in Cleveland Heights, University Heights and various different ambulances and fire departments. It’s a tragic shame all the people that were shot."
ABC News' Juwon Funes contributed to this report.