Two people — including a 16-year-old boy — were struck by bullets in East Harlem Tuesday afternoon in what police said was a burst of gang-related gun violence tied to the earlier shooting of a student on the West Side.

The teen and four other students at Harlem Renaissance High School were going out for lunch at around 1 p.m. when three men came up to them and a fight broke out between the two groups at East 129th Street and Madison Avenue, police officials said.

Bullets flew during the brawl — striking the teen in the leg. A 27-year-old man — an innocent bystander — was also shot in the leg and rushed to Harlem Hospital, according to cops.

Police sources said the violence could be a retaliatory strike stemming from an earlier shooting that locked down two Big Apple high schools on the Upper West Side just three hours earlier.

A 17-year-old high schooler was shot at least three times during a fight with other teenagers at Amsterdam Avenue and West 68th Street at around 9:50 a.m. — with the alleged 19-year-old shooter later busted.

That shooting forced two nearby schools — The Maxine Greene High School for Imaginative Inquiry, which the victim attends, and LaGuardia High School of Music — to go into lockdown.

The wounded teen was rushed to the hospital and was in stable condition after undergoing surgery, according to police.

Police said the two incidents — and a third shooting at East 105th Street and Park Avenue at around 3 p.m. — are all believed to be connected.

“We’re proceeding as if this is all connected,” NYPD Chief of Patrol John Chell said at a news conference on the Upper East Side.