SYDNEY - Australian authorities restricted movement and tightened curbs on gatherings in Sydney on Wednesday, hoping to avoid a coronavirus "super spreader" event during the city's New Year's Eve celebrations, after detecting a new cluster of cases.

Household gatherings were limited to just five people while the maximum number of people allowed to gather in public was capped at 30. Residential care facilities were closed to visitors.

"We don't want New Year's Eve to be the cause of a super-spreader," New South Wales state Premier Gladys Berejiklian said as she announced the restrictions would take effect from midnight on Wednesday "until further notice".

Berejiklian reported 18 new COVID-19 cases on Wednesday, the biggest daily increase in a week, with just half part of an outbreak in the city's northern beaches that has grown to more than 100 people over the past week.

NSW Chief Health Officer Kerry Chant said a new cluster in the city's inner west, which includes six members of an extended family living in three different households, is expected to grow as members had joined Christmas gatherings.

The outbreaks in Sydney have dampened the city's New Year's Eve harbour fireworks display, an event televised around the world.

In addition to the new restrictions, authorities have imposed a "green zone" in key vantage spots around the harbour that will be restricted to residents and people with confirmed hospitality bookings who apply for and receive a permit.

The usual 9 p.m. fireworks have been cancelled and the annual midnight session has been cut to seven minutes.

"If I can stress again, the strongest message to everybody across New South Wales no matter where you are, is please limit your activity and your mobility," Berejiklian said.

Australia has reported just over 28,300 COVID-19 cases and 909 deaths since the pandemic began.

(Reporting by Renju Jose) ((; +61 2858 77243;))