Under the Gothic spires of St John's College, women in gowns and men in dinner suits danced into the night to celebrate the end of the year.

They ate hamburgers and gelato, and lined up at an open bar serving champagne, beer and cocktails.

Jean Claude Perrottet, the younger brother of NSW Treasurer Dominic Perrottet, was at the ball as a guest of a college resident, and spent the evening drinking, dancing, and having a political argument with "a leftie".

A 19-year-old woman got ready with friends, drank champagne, and was spotted running into the crowd and dancing like "crazy" at the end of the night.