A 16-year-old armed with a semiautomatic assault rifle fatally shot his parents, sister and a family friend in a gruesome burst of violence that took place just before the start of the New Year, officials in New Jersey said Monday.

The teenager, who was not identified, was taken into custody by the police and is expected to be charged with four counts of murder, Monmouth County Prosecutor Christopher J. Gramiccioni said at a news conference on Monday morning.

The incident unfolded around 11:43 p.m. at the family's house in Long Branch, a small beachside town about 45 minutes south of Newark. Officials did not say what sparked the outburst.

The emergency call came from within the house, Gramiccioni said. The teenager's grandfather and brother were able to escape; officials do not believe they were targeted.

All four victims died on the scene, Gramiccioni said. They were identified as Steven and Linda Kologi, 44 and 42; Britney Kologi, 18, the suspect's sister; and Mary Shultz, 70, a family friend who lived in the house.

"We are investigating this and are confident that it's a domestic incident, that it's completely isolated," Gramiccioni said.

The weapon, which officials described as a Century Arms semiautomatic rifle, was registered to a family member at the house, Gramiccioni said. He said the arrest of the 16-year-old was "uneventful."