Bill English sworn-in as New Zealand's new PM

New Zealand's former deputy prime minister and minister of finance Bill English has taken charge as the country's 39th Prime Minister.

He replaced former prime minister John Key to become the new leader of the National Party.

Key, who had led his party for 10 years and the country for eight, unexpectedly resigned on December 5 and since then the position had become vacant.

"I am both excited and humbled by this opportunity. As Prime Minister, I will be committed to building a New Zealand which rewards hard work and enterprise and which cares for our most vulnerable," CNN quoted English, as saying in a statement.

Paula Bennett is the new Deputy Prime Minister and Deputy Leader of the National Party.

She was earlier the minister for climate change, social housing and state services.

Key said that he stepped down to spend more time with his family.

"Ten years at the top is a long time," he said, as he announced his shock resignation. "A lot of leaders stay at the top too long."

He said that his adult children had faced "an extraordinary level of intrusion and pressure because of their father's job.