A US teenager has been arrested after his family were found shot dead in their home on New Year's Eve.

Police responded to a report of shots fired at a house in Long Branch, New Jersey, shortly before midnight.

On arrival, they discovered the suspect's father, mother, sister, and a family friend had all been killed.

"It appears the 16-year-old boy used a Century Arms semi-automatic rifle", a statement from the Monmouth County prosecutor said.

The teenager, whose name was not released, was taken into custody without incident.

Authorities say he is expected to be charged as an adult with four counts of murder and one count of possession of a weapon for an unlawful purpose.

Information regarding a possible motive was not released, but the prosecutor's office described the shooting as an isolated domestic incident.

They added that the suspect's grandfather and brother were not targeted in the attack and left the home unharmed.

Prosecutors named the victims, but chose not to identify the alleged perpetrator.

Long Branch is a coastal town with a population of more than 30,000 people. It is around 55 miles (88km) south of New York City.