Prime minister of New Zealand John Key to resign due to family reasons

New Zealand's hugely popular prime minister John Key has unexpectedly announced his intention to resign from his position next week.

Key was elected in 2008 having taken over as leader of the National party two years beforehand, and told a press conference in Wellington on Sunday that it was the "hardest decision I've ever made."

The country is due to hold elections next year and Key was widely expected to run for a fourth term, but deputy prime minister Bill English is now expected to take over on an interim basis until the new year.

"This has been the hardest decision I have ever made and I do not know what I will do next," said during the speech.

Reports have alleged that Key had been given an ultimatum by his wife Bronagh, as the first family faced difficulties associated with being in the national spotlight.

Key acknowledged that becoming prime minister had changed his family life, and that it was a factor in his decision to resign, but stopped short of attributing all of the responsibility for it to this factor.

"It would be easy to say I have made this decision solely to rediscover the personal and family life I once had, and that is a factor, but it is one among many," he said.