A 16-year-old boy on a bicycle was shot once in the chest in front of a Mattapan church yesterday, police at the scene said, and an hour later while cops processed the scene, more gunfire rocked the neighborhood.

The shooting happened about 6 p.m. on River Street in front of the Church of the Nazarene, a Haitian church.

A 71-year-old man who lives across the street from the shooting scene said he was outside on his porch when he heard four gunshots.

“I was just outside enjoying the day. I get tired of watching TV. I come outside. I get tired of outside, I go in and watch TV,” the man said. “I heard four gunshots and I looked over and I saw a man run up Idaho Street.”

He said he did not see the victim.

The teen was taken to Boston Medical Center, and police said he is expected to live. The shooter has not yet been arrested, police said.

Witnesses told police the boy was chased down the street on his bike and shot as he fled. Police found four shell casings at the scene.

While police were at the scene and canvassing the neighborhood for witnesses, more gunfire popped about a block away.

Cops at the shooting scene ran about 100 yards to Groveland and Manchester streets, where they found seven shell casings. At the same time, police intercepted a car driving away from the shooting, police said. The car was hit four times on the passenger’s side. The passenger, who had outstanding criminal warrants, was arrested, police said.

Police said it is unclear if the gunplay was related to the earlier shooting of the boy on the bike.

A couple who live at the intersection stood on their front lawn and watched the cops. They said their car was struck by one of the bullets. Detectives roped off the Hyundai with crime scene tape and put a yellow cone on the trunk above a flat tire.

The car’s owner said he was in the living room of his brick house when he heard the gunfire.

“I was sitting right there,” he said pointing to the spot in his house closest to the damaged car.

His wife shook her head.

“How are you going to get to work tomorrow?” she said.

Neighbors said the violence was unexpected on their end of River Street.

“I’ve lived here since ’82,” said a man who declined to give his name. “I’ve never seen anything like that around here. There’s not that much drug activity. I’d say it’s kids being crazy. It’s not like a drug-turf thing.”

No arrests have been made in the boy’s shooting. Anyone with information is asked to call Crimestoppers at 800-494-TIPS or text a tip to CRIME (27463).