John Key has been officially sworn in as Prime Minister in a ceremony at Government House.

In all, 27 ministers were sworn in by Governor General Sir Jerry Mateparae. Four of them were taking the ministers' oath for the first time - National's Maggie Barry, Louise Upston and Paul Goldsmith, and the Maori Party's Te Ururoa Flavell.

Mr Key said the new ministers should "savour the moment" because they had a huge workload in front of them.

"The workload of a minister of the Crown is enormous. It demands great sacrifices from your family and you do that with their blessing."

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He said they would have some "good days and some bad" but "every day in government is a lot better than a day in opposition".

Mr Key said he was not thinking about the troubles he had with his Cabinet in the last term, during which five ministers were forced to resign for various scandals.

"Today's a day of celebration and a day to reflect on the responsibility that the New Zealand public bestowed upon us when they effectively put National back ... in government."

Cabinet's first priorities would be housing and education reforms, getting back into surplus and considering problems in the Middle East.