The passengers were returning from a wedding at a winery on Sunday night when their coach overturned on Wine County Drive near Greta in Hunter Valley, New South Wales.
Police say they are investigating the circumstances surrounding the crash.
The driver of the bus, a 58-year-old man, has been arrested.
NSW Police Acting Assistant Commissioner Tracy Chapman said the guests were travelling to Singleton "presumably for their accommodation". The crash occurred around 23:30 local time.
