By Rowan Quinn for RNZ
Four travellers have been fined for coming to the country without a pre-departure Covid-19 test.
Since mid January, people arriving in New Zealand from most countries have had to prove they had a negative test before their flight - or risk a fine of up to $1000.
Customs figures showed the vast majority of the roughly 15,000 people who arrived had complied.
But it had also issued 33 warnings - most of them shortly after the rule was introduced.
Ten people who arrived on the same flight with Covid-19 this week all had pre-departure test certificates.
The Ministry of Health said the quality of testing varied around the world and it was looking into whether some of those cases were historical.
Fake pre-departure certificates were not "regarded as a significant issue", a spokesperson said.
There was little solid evidence of the benefits of pre-departure testing to keeping numbers low in managed isolation, she said.
"A traveller can return a completely authentic negative test before travelling, but won't catch a diagnosis particularly during the early stages of infection," she said.
A managed isolation and quarantine spokesperson said they knew of 40 people who had cancelled their spot in managed isolation because their pre-departure test had been positive.
Prime Minister Jacinda Ardern said the 10 cases highlighted the shortcomings of pre-departure tests which could be done 72 hours before people left.