More than 10 of the 15 Sydney dock workers who boarded a ship found to have COVID-positive crew have tested negative for the virus.
The Inge Kosan, an LPG tanker, was docked in Port Botany for a day from March 31 after arriving from the Papua New Guinea capital of Port Moresby.
It then sailed for Vanuatu on April 1.
"Health authorities in Vanuatu have confirmed that 12 out of 13 crew members from the ship, including (a) deceased crew member, tested positive for COVID following testing in Port Vila," NSW Health said in a statement on Friday.
Some 15 wharfies boarded the vessel when it was at Port Botany more than three weeks ago and 11 have since tested negative.
The remaining four are awaiting their results which are expected on Friday.
NSW Health said none of the crew of the Inge Kosan left the ship when it was in Sydney and the wharfies who boarded it were wearing protective gear.
Health authorities are also interviewing two additional Sydney port workers to determine whether they also boarded the Inge Kosan.
The Maritime Union of Australia nevertheless demanded National Cabinet convene to improve testing and biosecurity measures for arriving vessels.
The MUA's demands include the introduction of rapid testing for arriving seafarers and the declaration of Australian maritime workers as "key workers", making them eligible for vaccination.
"The current arrangement, where COVID testing only takes place if a ship self-declares symptoms, is completely flawed and needs to be urgently overhauled," MUA national secretary Paddy Crumlin said.
NSW Treasurer Dominic Perrottet told reporters on Friday that he had full faith the Inge Kosan matter would be quickly resolved.
The state recorded zero new local cases in the 24 hours to 8pm on Thursday as well as 18 new cases in hotel quarantine.
"We have the best health testing teams not just in the country but in the world, I have complete confidence they'll get to the bottom of this as soon as possible," Mr Perrottet said.
"It's early days but ultimately we want to make sure we keep our people safe, and we'll act on the health advice we receive."
Meanwhile, NSW authorities are still trying to locate four people who may have been exposed to COVID-19 at a Sydney quarantine hotel.
Up to 40 returned travellers and some hotel staff may have been exposed to the virus earlier this month.
NSW Health has contacted 36 of those people and is urgently trying to find the other four.
The potential quarantine breach was revealed Wednesday night after three returned travellers who stayed at the Mercure Hotel in Sydney were diagnosed with the same South African strain of the virus.
The travellers were family members who had stayed in connecting rooms on the 10th floor of the Mercure Hotel, while the third person stayed in another adjacent room.
NSW Chief Health Officer Kerry Chant said some hotel guests had since travelled to other states and territories and authorities there had been alerted.
Anyone who stayed on the 10th floor of the Mercure between April 7 and April 12, should get tested and self-isolate until 14 days after they left quarantine.
Authorities are still investigating how the breach occurred.
A separate case of transmission between hotel rooms at the Adina Apartment Hotel at Town Hall is ongoing, and all contacts located so far have tested negative.
Meanwhile, a Victorian man has tested positive for COVID-19 after contracting the virus in hotel quarantine in Perth, bringing the southern state's eight-week run without a locally-acquired case to an end.
Australian Associated Press