A Bushwick High School student who just celebrated his 16th birthday was stabbed in the stomach as he left school Tuesday afternoon, police sources said.

The student, whose birthday was Monday, was stabbed moments after he and several other students spilled out of the Putnam Avenue school in Brooklyn about 3 p.m., sources said.

The victim and his group, which police described as “disorderly,” was being monitored by officers on patrol as they made their way down Putnam before several of the students encountered another gathering, cops said.

The teen was stabbed by a 22-year-old assailant who was quickly arrested by police. Charges are pending.

The victim was rushed to Woodhull Hospital in stable condition, where he was undergoing surgery, sources said.

It’s unclear what sparked the violence, and the investigation is ongoing.

The incident comes one day after another city high-school student was stabbed in the stomach near the Barclays Center in Brooklyn. That victim, also 16, suffered non-life-threatening injuries in the 3:30 p.m. attack.