SYDNEY (AFP) - Dancing, singing and chanting were banned across Sydney in a fresh round of restrictions introduced on Sunday (Dec 20) as Australian authorities raced to control a growing coronavirus outbreak in the city.

As hundreds of thousands of people on Sydney's northern beaches awoke to the first day of a snap lockdown, authorities announced another 30 coronavirus cases had been detected in the area.

That brings the Covid-19 cluster in Australia's most populous city to 68 cases since it emerged on Thursday (Dec 17), causing alarm among health officials, who issued stay-at-home orders for several beachside suburbs.

New South Wales state - which incorporates Sydney - on Sunday announced bans on dancing, singing and chanting at indoor venues across the city except at small weddings and religious services.

"It is the season when we all love to be singing," State Health Minister Brad Hazzard said.

"But for the moment, it is probably one of the most dangerous exercises you can do, dancing and singing."

Sydney restaurants, bars and cafes will be forced to limit patron numbers to 300 people, while caps have also been placed on visits to homes.

Mask-wearing is being encouraged, but has not been made compulsory.

Officials have promised to review the rules on Wednesday in the hope some restrictions can be lifted before Christmas Day.

The latest outbreak has thrown Christmas plans into disarray, as many Australians who hoped to reunite with family after long separations were forced to cancel travel after new domestic border closures.

On Sunday, Victoria and South Australia became the latest states to announce Sydney residents would be subject to mandatory hotel quarantine for 14 days on entry.

Australia has largely been successful in containing the virus, taking an aggressive approach centred on imposing early and often far-reaching restrictions in response to new outbreaks.

The country has recorded just over 28,100 Covid-19 cases and 908 deaths in a population of about 25 million.