A 16-year-old from Bellingham was shot and killed at a large party in Northborough, prosecutors said

According to Worcester County District Attorney Joseph Early Jr., a 16-year-old Bellingham male was shot and killed at a large party in Northborough early Sunday morning.

Three adults have been arrested on firearms charges in connection with the shooting, but no murder charges have been filed so far, the district attorney said during a news conference Sunday afternoon. The suspects are all in their late teens or 20s and none are from Northborough.

Authorities began investigating the shooting after a partygoer flagged down a Northborough police officer around 1 a.m. Sunday morning and told him that a person at the party at 333 Howard St. was brandishing a gun, Early said. More than 25 officers from eight different departments – including the Massachusetts State Police – prepared to enter the home when they heard gunshots.

Police then stormed into the house – where about 300 people had gathered – and found the 16-year-old who had been shot, Early said. They provided medical aid at the scene before taking him to an ambulance. He was taken to UMass Memorial Medical Center in Worcester, where he was pronounced dead.

A second victim – a 17-year-old male – was shot in the buttocks, Early said. He was taken to Marlborough Hospital and later released. Two other injured people were taken to Marlborough Hospital with non-life-threatening injuries and several others were treated at the scene but refused hospital admission.

The three suspects were arrested at the scene on firearms charges and are scheduled to be arraigned in Westborough District Court on Monday, Early said. The district attorney did not identify any of the victims or suspects during Sunday’s news conference.

“Our thoughts are with the victim and his family during this senseless act of violence,” Northborough Police Chief Brian Griffin said during the conference. “It’s especially difficult since it’s Mother’s Day.”

Northborough police were notified last month of a large party at the home, Griffin said. Officers spoke with the homeowner, who told them there would not be another such gathering.

The homeowner — a man police did not identify — was inside the house during the party, Griffin said. It’s unclear what percentage of partygoers are underage, Early said.

The eight police departments are still investigating the shooting, and the investigation is in its early stages, Early said. Investigators are asking anyone with information about the shooting to call Northborough police at 508-393-1515.