Sydney, Dec 30 (IANS): Sydney on Wednesday reported 18 new locally acquired coronavirus cases, raising concerns that an already active Covid-19 cluster could further increase.

Half of the new cases are located outside the cluster area of Sydney's Northern Beaches, with six linked to a family in the inner west suburb of Croydon and three under investigation, Xinhua news agency reported citing health authorities as saying.

Contact tracers were unable to link the six cases in Sydney's inner west to a known source and concerns were raised over the family's movements during the Christmas period which saw 34 other people identified as close contacts.

"We are expecting that there will be additional cases linked to that cluster just because of the number of close contacts they had over the period of Christmas and the preceding days," New South Wales (NSW) Chief Health Officer Kerry Chant said.

Meanwhile, two of the cases under investigation were detected in the city of Wollongong, 70 km south of Sydney.

One of the infected individuals had travelled to Sydney in mid-December and visited locations in the city centre, prompting warnings for those who had been in the same area.

The nine additional cases linked to the original cluster took its total to 138, with the area remaining in lockdown until at least January 9, 2021.

Outside the lockdown area, limits on outdoor gatherings in Greater Sydney were reduced from 50 to 30 people, while the maximum numbers of visitors allowed in households dropped from 10 to five.

"Our preferred advice is that people just stay home for New Year's Eve, but if you must have people over, don't have more than five and please make sure you have adequate social distancing, good ventilation," NSW Premier Gladys Berejiklian said.

The state of NSW currently accounts for 4,906 coronavirus cases and 54 deaths.

Australia has so far reported a total 28,350 cases and 909 fatalities.