Police injured at wild Sydney 18th party

A teenager has been charged after police were attacked and injured at an out-of-control 18th birthday on Sydney's northern beaches.

Police say they were called to a home in Ernest Street at Balgowlah Heights at about 10pm on Saturday, where they were confronted by more than 250 drunken teenagers.

Two were injured when they tried to calm some of the revellers.

One officer fractured his hand and the other injured his shoulder. Both were treated at the scene by paramedics and taken to hospital.

A third officer was struck in the head by a bottle that was thrown outside the home but he was not injured.

A 17-year-old was arrested at the party, taken to Dee Why Police Station and charged with assault, resist officer, trespass and affray.

He was granted bail to appear at a children's court.