NSW has reintroduced social distancing measures after recording 16 new locally acquired Covid-19 cases, half of which were linked to a birthday party in Sydney's south-west.
Chief health officer Kerry Chant said 14 of the new infections were linked to the Bondi cluster - which now sits at 31 - but two of the cases were unlinked.
"The cause of our concern is that we have had people infectious is in the community unknowingly," Dr Chant said.
Premier Gladys Berejiklian introduced new social distancing restrictions in response to Sydney's growing Covid-19 outbreak, including a limit of five guests in a household, and masks will be compulsory in all indoor non-residential settings.
NSW Health said the restrictions would be in place for one week.
A Syndey traveller to New Zealand has tested positive for the virus upon their return to Australia.
Health authorities believe the case's infection started before they left for New Zealand and have decided enforce a higher alert level in Wellington, where the visitor went.
New Zealand also paused the travel bubble with NSW last night.
Queensland and Victoria close borders to some Sydney council areas
Queensland has declared more New South Wales local government areas Covid-19 hotspots as the southern state's cluster of the highly infectious Delta variant grows.
Premier Annastacia Palaszczuk said as of 1am on Thursday, Queensland will close its borders to Sydney, Bayside, Woollahra, Canada Bay, Inner West and Randwick council areas.
The state already declared the Waverley Council area a hotspot.
Travellers from those areas would be barred from entering the state, while Queenslanders returning from those areas will be placed in hotel quarantine.
Non-Queensland residents who visited those areas would need an exemption to enter the state and would also need to quarantine.
Victoria's Chief Health Officer declared the same seven local government areas in New South Wales as red zones, effective from 1am on Wednesday.
Victorian residents who have been in a red zone can obtain a permit to re-enter the state but must quarantine at home for 14 days.
Non-Victorian residents cannot enter the state if they have been in a red zone.
Travellers who have passed through a red zone without stopping can apply for an entry permit.
Concern over Delta variant
Premier Annastacia Palaszczuk said she had "serious concerns" about the Delta variant which originated in India and warned people to be prepared for advice to be updated later in the day if the New South Wales cluster worsens.
It comes as Queensland recorded no locally acquired cases of Covid-19, but recorded an overseas case of the Delta variant in hotel quarantine.
Meanwhile, health authorities have been investigating how the virus was transferred between hotel quarantine guests at the Novotel Brisbane Airport earlier this month.
Dr Young said the transmission occurred between returned travellers in two adjacent rooms on the fifth floor.
"At the time, we thought it was just overseas acquired, but now that I've got the genome sequencing back it's clear that the first person has given it to the other two," she said.
"We're contacting all of the 30 people on floor five and anyone who left quarantine during the period that I'm concerned about.
"The people on floor five, their stay is being extended until we've been able to confirm that there's been no additional transmission."
- ABC / RNZ