The Berejiklian government is warning young people that unless they curb their socialising they will spread the coronavirus, as backpacker hostels were still hosting parties on Friday night despite tough new restrictions.

More than one third of NSW’s 1405 coronavirus cases are people aged in their 20s and 30s, prompting concerns other young people with mild or no symptoms could be unwittingly spreading the virus.

Police leave the Bondi Beach Backpackers after breaking up a public indoor gathering on Friday night. Credit:Cole Bennetts

NSW Police Minister David Elliott described the decision by hostels to hold parties as "one of the most irresponsible things I have ever come across" and warned police would have no hesitation handing out fines of up to $5000.

“If these people think they can gather for a barbecue at a backpackers in Bondi on a Friday night, they will face the full force of the law,” Mr Elliott said.