A 17-year-old boy has drowned while swimming at a beach on the NSW mid-north coast.

Emergency services were called to the unpatrolled Diamond Beach, north of Forster, about 1pm on Wednesday after reports that a boy who was swimming with his family had gotten into trouble.

Police pulled the teen from the water and performed CPR until paramedics arrived.

Despite their efforts, the boy died at the scene. A report will be prepared for the coroner.

-with AAP