A Greymouth police officer was assaulted and taken to hospital on Saturday night as police dealt with 21 unruly youths, some as young as 13, after a Facebook message about a beach party sparked a night of drunken bedlam in the town.

The officer was attacked as police tried to gain control of a group of drunken youths, Senior Sergeant Allyson Ealam said. The officer, who was trying to arrest a drunken male for breaching the peace, was taken to hospital after part of his ear was nearly cut off and he suffered cuts to his head.

The male was arrested and charged with assaulting police, disorderly behaviour and resisting arrest.