Sydneysiders will again be forced to wear their masks on public transport and New Zealand has halted flights from NSW after two new COVID-19 cases set the state on edge again.
Quarantine-free travel between New Zealand and NSW is on hold for two days from midnight while NSW health authorities investigate the "missing link" between a coronavirus-positive traveller in hotel quarantine and an infected Sydney man.
New Zealand's COVID-19 Response Minister Chris Hipkins blamed "several outstanding unknowns" as he announced the travel bubble pause on Thursday afternoon.
"We've weighed this up very carefully, it's a finely balanced decision, because we do acknowledge that this has the potential to disrupt people's travel," Mr Hipkins told reporters.
Restrictions are back in the Greater Sydney area from 5pm on Thursday, with masks compulsory at all public indoor venues and on public transport. Visitors in homes are capped at 20.
Singing or dancing indoors is banned, with an exception for weddings, where numbers on the dancefloor will be limited to 20.
Drinkers in bars must be seated and just two visitors will be allowed for residents in aged care homes.
The restrictions - which extend to the Blue Mountains, the Central Coast and the Illawarra - will remain in place until at least Monday morning.
The measures were announced as Premier Gladys Berejiklian revealed that a man in his 50s from Sydney's east, who was diagnosed with COVID-19 on Wednesday, had infected his wife but no other close contacts so far.
Health detectives established that the man has the same COVID-19 strain as a man who travelled from the US and was diagnosed in hotel quarantine. There is no link between the pair.
"If we'd been able to identify the case in between, the missing link or links, of course we would've taken a different approach," Ms Berejiklian said.
"But we know for a fact there's at least one person, if not more, walking around with the virus, not knowing they have it or potentially having attended many events and venues ... this is a proportionate response."
The NSW premier was keen to emphasise the city remains open for business, particularly with Mother's Day looming on Sunday.
"Unlike other premiers, we're not shutting down the city," she said.
"If you've got a booking (this weekend), go to the booking, enjoy Mother's Day, do what you would normally do."
She said other premiers should not close their borders to NSW. None have defied her so far.
Queensland and WA will send anyone who has visited an exposure site in Sydney into 14-day hotel quarantine from 1am on Friday.
Those who've been to exposure sites won't be allowed into Tasmania. Anyone in Victoria or the ACT who's potentially been exposed has been asked to self-isolate.
NSW Health believes the unvaccinated Sydney man diagnosed on Wednesday has been infectious since last Friday.
A list of nearly 20 venues of concern has been compiled which extends to the city's east, west and north.
People who have attended the listed venues at various times between Friday and Tuesday should get tested and self-isolate until they receive further advice.
On Wednesday evening NSW Health reported that fragments of the virus had also been detected in the Marrickville sewage network in Sydney's inner west.
But they are yet to uncover any virus-positive cases in the area.
Australian Associated Press