Non-essential travel outside of Sydney has been banned and masks made mandatory everywhere after NSW today recorded 16 new locally acquired Covid cases.

There are now 37 cases linked to the Bondi cluster.

Of the new cases, eight attended a party in Sydney's eastern suburbs, NSW Premier Gladys Berejiklian said at a media briefing this afternoon.

One of the cases is a person who was in the same waiting room as a previously known case, and four are under investigation, "but all are in close proximity to the southeast Sydney cluster", Berejiklian said.

Today's numbers come after NZ health authorities revealed a Covid-positive Australian man had travelled on a Qantas flight from Sydney to Wellington on June 18 and returned home on an Air NZ flight on June 21.

The Wellington region will go into Alert Level 2 from 6pm tonight. A list of New Zealand exposure sites was released this morning.

Expert calls for lockdown

Yesterday, NSW Health recorded 10 new locally acquired cases, taking the Bondi cluster total to 21.

New mask restrictions were brought in yesterday, but epidemiologist and World Health Organisation adviser Professor Mary-Louise McLaws suggested a lockdown would add another layer of protection.

"We may need to think about a stay home order for a couple of days. I'm sure the authorities will feel quite confident by Saturday," McLaws told ABC's News Breakfast today.

McLaws said a "quick, sharp stay at home order" would give authorities time to identify any other potential chains of transmission.

All but one of the cases announced yesterday were either linked to a known exposure site, a close contact of a case or a household contact of a case.

The one infection that is yet to be linked to the Bondi cluster is a child from St Charles Catholic Primary School in the Sydney suburb of Waverley.

An urgent investigation is under way into the source of the infection, with health authorities focusing on those linked to the primary school and its wider community.

text by Ally Foster, news.com.au