Several Pacific nations are preparing to open up foreign travel restrictions to neighbouring islands and New Zealand.
But Tonga, which was one of four of the countries that have been included in the agreement, could be locked out on November 8.
The government announced on Monday that Tongatapu island will go into lockdown as of midnight until at least Sunday.
The move comes after Tonga was one of the seven last nations in the world not to have recorded a Covid-19 case that includes Niue, Tokelau and Tuvalu.
Its first case was confirmed on Friday after a returning traveller from Christchurch tested positive on arrival before heading into mandatory 21-day quarantine.
It remains uncertain whether travel from the most populous island to Samoa, Vanuatu, Tokelau or New Zealand can resume when the one-way travel bubble begins the next day.
Travellers from the Pacific are required to be fully vaccinated before departing, New Zealand Covid-19 response minister Chris Hipkins said, unless they are from New Zealand.
Pacific seasonal workers from the countries will be allowed fly with just one dose of the vaccine but would need a second dose by January 1.
Standard quarantine-free travel requirements will remain in place for passengers to confirm they have met New Zealand’s health and eligibility requirements.
“I thank the governments of these countries for their co-operation, which has led to us reaching this positive step in reconnecting our people, and the horticulture industry for the initial successful trial of QFT with Tonga, Samoa and Vanuatu,” Mr Hipkins said in a statement.
Existing arrangements with the Cook Islands and Niue will be maintained.
Their borders remain closed, but both governments have resumed repatriation flights for stranded citizens in New Zealand.
“The Covid-19 situation continues to evolve rapidly, both here and abroad,” Hipkins said.
“We need to move quickly to make sure we’re minimising the risks we face in the best way possible. We will, as we always have, step through these changes carefully.”