New Zealand Police Minister Judith Collins said today she will stand as a candidate to replace outgoing Prime Minister John Key, becoming the third cabinet member to announce their candidacy.

Key, who is part-way through a third, three-year term that has been marked by political stability and economic reform, announced his surprise resignation yesterday, saying he wanted to spend more time with his family.

Earlier, Finance Minister Bill English, who is considered the front-runner to replace Key, and Health Minister Jonathan Coleman announced they would contest the National Party leadership in a caucus meeting on Monday, Dec 12.

English, a former Treasury Department analyst who is also deputy leader of the ruling centre-right National Party, is viewed by both lawmakers and political analysts as the front-runner for the top job.

"I can see fantastic opportunities for stronger economic performance, for spreading the benefits of growth for more New Zealanders... I am a candidate for leadership," English told reporters after a caucus meeting in New Zealand's distinctive 'Beehive' Parliament building in the capital, Wellington.

However, Health Minister Jonathan Coleman also said he would run to replace Key, and other prime contenders have so far refused to say whether they would make challenges of their own.

Other potential candidates include senior cabinet minister Steven Joyce and fellow cabinet minister Paula Bennett.

A recent UMR survey of voters pegged English as the most favoured replacement for Key on 21 percent, followed by Joyce on 16 percent, Bennett on 11 percent and Collins (photo) on six percent.

Coleman was not ranked in the survey, which was conducted in early October, before Key's resignation, but confirmed he would put his name forward at a caucus meeting on Monday, when a ballot for the leadership will be held.

"I am seeking the party leadership and I am absolutely up for the challenge. I believe I have got the energy, I have got the relative youth on my side and I am absolutely focused on winning this leadership contest," Coleman told reporters.

Key, who has been New Zealand's leader since 2008, is backing English to be the formal candidate ahead of Monday's leadership ballot.

The National Party is part-way through a third, three-year term that has been marked by political stability and economic reform.

Praised for his stewardship of New Zealand's $170 billion economy in the aftermath of the global financial crisis and two devastating earthquakes in Christchurch, the largest city on New Zealand's South Island, Key remains one of the world's most popular leaders.

Moody's Investors Services said it did not expect to change New Zealand's Aaa credit rating as a result of Key's resignation, adding it expected the country's "very strong institutions to lead to a smooth tradition and policy continuity".

National elections are not expected until late 2017.

- Reuters