An expert is calling for tighter checks on travellers leaving New Zealand soon after arriving here in the wake of news that hundreds of new arrivals have left for Australia.
Statistics NZ has confirmed that 549 people who arrived in New Zealand on or after October 1 left for Australia in October or November.
Most of them (492) were NZ residents, and many are believed to be air crew and business people who are still travelling regularly despite Covid restrictions.
But Auckland University's Professor Shaun Hendy, who has been modelling the risks of international travel during the Covid-19 pandemic, said the figures showed the need to keep track of everyone leaving quarantine in case there was another outbreak in the community.
"We should be better at following up with travellers and understanding where they are going," he said.
"If we ever did consider the situation where we were asking for follow-up [in a community outbreak], then we would want to be able to ask people to come in for those tests and for follow-up interaction with the border system, so it would be important to know whether they have remained in New Zealand or not."
The latest figures emerged after Australian authorities said that 12 people who had been in quarantine at Auckland's Pullman Hotel at the same time as a person who caught Covid there last month had travelled to Sydney.
Three of them travelled on from Sydney to Hong Kong, two went to Queensland and the other seven stayed in New South Wales.
Statistics NZ said 549 people who arrived in New Zealand after October 1 left in October or November - 39 in October and 510 in November, the latest figures available.
Australia allowed New Zealanders to travel without quarantine to New South Wales and the Northern Territory from October 16, to South Australia from October 20, to Victoria from November 9 and to Queensland from December 12.
New Zealanders travelling to Western Australia still have to quarantine for 14 days.
The 549 people who arrived in New Zealand after October 1 and travelled to Australia before the end of November represented 2 per cent of the 24,133 people who arrived in New Zealand in those two months, and about the same proportion of the 27,106 people who left the country in those months.
Almost all (492) of the 549 people were NZ residents, with only 57 residents of other countries entering New Zealand after October 1 and leaving by November 30.
Statistics NZ population indicators manager Tehseen Islam said the 549 arrivals who travelled on to Australia included air crew, who must have Covid tests every seven days but do not have to quarantine for 14 days.
Covid Response Minister Chris Hipkins said he has asked officials "to consider the overall process and to explore whether the system can be modified so that those who leave quickly for Australia could and should pay a premium for their stay in MIQ".
"I've seen no evidence of any particular motivation for why people travel on to Australia in the months after landing in New Zealand," he said.
"There is likely to be a variety of reasons, and the travellers could include a number of New Zealand citizens.
"We need to strike the right balance of acknowledging people's rights to free movement with fairly managing the finite resources of MIQ and Kiwis' right to come home."