A Catholic priest who allegedly abused 11 children at a New South Wales college 30 years ago now faces more child sexual abuse charges.

On Tuesday the 78-year-old, who is already before the courts after being charged in April with nine sexual and indecent assaults at a Southern Highlands boarding school, was rearrested and charged with another 18 offences.

These include sexual assault offences, indecent assault offences, and offences of gross indecency.

Police alleged between 1982 and 1989 the priest assaulted 11 children, and committed 27 offences in total. They alleged his victims were aged between 12 and 15.

The priest managed a dormitory at a Southern Highlands college in NSW, and was also a rugby coach and band teacher. The abuse is alleged to have occurred in the 1980s.

Detectives from the Hume police district and strike force Caber began investigating in July 2018.

The man, from Kensington in Sydney, has been given conditional bail to front Moss Vale local court on 8 October after being rearrested at 11.30am on Tuesday.

Police are urging other victims of child sexual abuse to come forward.