The resignation of Prime Minister John Key also came as a complete surprise to Rotorua MP and Trade Minister Todd McClay.

Mr McClay spoke to the Rotorua Daily Post from Iran, as he was about to board a plane to New Zealand following a trade trip.

"It was a surprise but John Key always said that he would do the job as long as he thought he had something to give."

Mr McClay said the National Party remained strong, despite today's shock news.

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"[It is] the strongest I remember it since I have been involved in the National Party."

He said there were a number of people in the National Party Caucus who would be able to step forward and take on the leadership and lead the party into the next election.

When asked if he would put his hand up for the job, Mr McClay replied: "no".

But he said he looked forward to helping select the new leader early next week.