A bullet meant for someone else struck a 5-year-old boy celebrating his birthday late Monday afternoon in the Bronx, the NYPD said, leaving the child in critical condition at a Manhattan hospital.

“His condition is grave at this time,” said NYPD Asst. Chief Larry Nikunen.

The boy was being walked to a waiting car at about 5 p.m. after visiting his father on Washington Avenue, Nikunen said, when a man in his 20s fired at least four shots intended for another man. One bullet struck the child in the head, Nikunen said.

The NYPD said Tuesday morning that two males were being questioned.

The boy was taken to St. Barnabas Hospital before being transferred to New York-Presbyterian/Columbia University Medical Center, police said. He remained in critical condition Tuesday morning.

A ShotSpotter siren was activated afterward and ballistics have been recovered, an NYPD source said. Video surveillance footage from the area is being reviewed and the investigation is ongoing, the source said.

In a tweet Monday night, Mayor Bill de Blasio called the shooting “Absolutely heartbreaking.”

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“The city’s prayers are with him and the doctors working to save his life,” added de Blasio in the tweet.

Bronx Borough President Ruben Diaz Jr. called it “an incredible tragedy” on Twitter and asked people to “Please pray for this child’s speedy recovery.”

With William Murphy and Pervaiz Shallwani