US President Donald Trump's administration has sent its congratulations to Prime Minister in waiting Jacinda Ardern.

A statement issued by the US Department of State today congratulated Labour and Ardern "as she forms the next coalition government in New Zealand".

"The US-New Zealand relationship is strong and New Zealand is one of our closest friends and partners" the department said in a statement.

"We look forward to working with New Zealand's new government and continuing to cooperate on our shared interests in the region and worldwide."

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Ardern has already spoken to Australian Prime Minister Malcolm Turnbull, had a congratulatory Tweet from Canada's Justin Trudeau, and was scheduled to speak to British Prime Minister Theresa May last night.

The Labour leader is due to meet Trump in Vietnam at the Apec summit in three weeks' time.