AN 18th birthday party at Mollymook was gate-crashed by about 30 armed, uninvited guests highlighting the danger of posting party details on social media.
Two people were treated for cuts after being hit with glass bottles during the party on Saturday night.
A man and a woman received head injuries and a woman was punched in the face, after a group of about 30 gate crashers was asked to leave the party.
The event in Clissold Street had been registered with the police.
According to police the gate crashers arrived at the home about 10.40pm, and were allowed in by a young woman.
However, trouble started when they were asked to leave a short time later. An altercation started, but the unwelcome visitors fled when they were told police had been called.
People at the party said the gate crashers, who they claimed were armed with iron bars and tasers, might have been alerted to the party by someone posting details on Facebook.
When police arrived at the scene they arranged medical treatment for several injured people.
Police investigations into the incident are continuing, and anyone with information is asked to contact the Ulladulla Police Station on 454 8599, or Crime Stoppers on 1800 333 000.