The Prime Minister's first official visit to Japan got off to a bumpy start as she referred to the wrong country during an interview with media.

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Jacinda Ardern began her opening remarks saying "this is an incredibly exciting time for New Zealand and its relationship with China" – before a quick correction instead to Japan.

When asked about the misstep she simply put it down to jetlag having moments earlier touched down from New Zealand.

"You’ll understand I've been on continuous travel and just this moment stopped here," she joked.

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But the timing couldn't have been worse.

A report released the same day by the Asia New Zealand Foundation is questioning whether New Zealand has allowed its relationship with Japan to "drift" with the focus more on China.

"Perhaps we have taken the relationship with Japan a little bit for granted," Asia New Zealand Foundation executive director Simon Draper says.

Mr Draper says while the country's focus on China is understandable now is an opportune time to strengthen ties with Japan.

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"Because of the opportunities that have existed in the region, particularly around China, our energy has been going there."

But the Prime Minister was keen to downplay the report referring to the importance of creating a diverse range of export partners.

"Obviously China is our largest export market, but Japan coming in at fourth is an incredibly important market for us as well."