New Zealand has held 18th place in a global ranking of the "soft power" countries yield internationally, pointing to the impact of "Jacindamania" internationally.

The Soft Power 30 Index ranks the top 30 countries judged as having the greatest global influence through soft power such as diplomacy, international engagement and leadership rather than military power.

New Zealand was ranked at 18 again, but the report by the UK based consultancy firm Portland noted that did not mean it was an uneventful year and said Ardern has appeal both at home and abroad.

"Jacinda Ardern's optimistic and youthful spirit reflects a small but ambitious nation that punches well above its demographic weight.

Ardern has injected new life into Kiwi polity, a tough ask given the popularity of the country's two previous Prime Ministers."

It recommended Ardern use her popularity to "make good on promises for increased environmental protection."

"Global players such as France are looking for partners in protecting the climate and Ardern can propel New Zealand as a major voice on this issue."

In its verdict on New Zealand, the report notes that it had earlier recommended New Zealand should promote tourism more.

The report was positive about the role Ardern played in a Tourism NZ advertisement with comedian Rhys Darby about world maps that did not include New Zealand.

It said that "tongue-in-cheek" campaign was a step toward attracting visitors "and stepping further away from Australia's cultural shadow."

Ironically, the map used in the Soft Power 30 report itself does not have New Zealand on it.

It listed New Zealand's geographic isolation and small population as "barriers" for engagement, but steps were being taken to reduce those. "The West is also increasingly looking to New Zealand as a leader in Asia Pacific affairs."

It also noted the recent Budget decision to push aid into the Pacific.

It said Ardern could take credit for boosting New Zealand's international appeal, noting events such as Ardern wearing a korowai [cloak] to a banquet at the Commonwealth Heads of Government Meeting in April and becoming the second female Prime Minister to have a baby in office.

The index has been prepared for the past four years by UK-based strategic communications consultancy firm Portland and the University of Southern California Center on Public Diplomacy.

New Zealand's highest ranking was in 2016 and 2017 when it was 16th place, partly due to its place on the Security Council.

Since 2015, Australia has dropped from sixth place to 10th.

The top country in 2018 was the United Kingdom, which regained the slot after France leapt from fifth to first in 2017 after the election of Emmanuel Macron.

Since US President Donald Trump's election in 2016, the US has slipped from first to fourth.