New Zealand will open a travel bubble with the tiny Cook Islands this month, adopting quarantine-free arrangements similar to those already established with Australia, Prime Minister Jacinda Ardern said.

Ardern said the bubble with the South Pacific island state of about 20,000 people would open on May 17 and initially involve about three flights a week.

"Two-way quarantine-free travel is a significant step in both countries' Covid-19 recovery, and a direct result of both New Zealand and the Cook Islands' successful response to the pandemic," she said.

The remote Cook Islands is one of few places in the world to remain coronavirus-free, while New Zealand has eliminated community transmission and recorded only 25 deaths in a population of five million.

The Cook Islands is self-governing in "free association" with New Zealand, meaning that while it administers its own affairs, Cook Islanders are both New Zealand citizens and Cook Islands nationals.

As a result, there are more expatriate Cook Islanders living in New Zealand than on the islands.

"(The bubble) will mean families can reconnect, commercial arrangements can resume and Kiwis can take a much-welcomed winter break and support the Cook Islands' tourism sector and recovery," Ardern said.

A long-awaited travel bubble between New Zealand and Australia opened last month, and has been hailed as a major milestone in restarting a global travel industry gutted by the pandemic.

New Zealand opposition leader Judith Collins said Wellington should now prioritise opening travel bubbles with Tonga and Samoa, two Pacific island nations that have detected no community cases of Covid-19.