Replacing John Key: The contenders

UPDATE: Since this gallery was published on Monday 5 December, 3 candidates have confirmed they are running - Bill English, Judith Collins and Jonathan Coleman.

The National Party caucus will hold a meeting on December 12 to decide the new party leader and Prime Minister.

Newstalk ZB political editor Barry Soper said attention will now be turned to who will take over.

"Like Helen Clark, there's no natural successor in line, so this is indeed a big announcement from the Prime Minister, and totally unexpected."

Key said caucus has a number of fine individuals to choose from - but if Bill English puts his name forward - he will get his vote.

"Bill has I believe grown a great deal since he was last the party leader."

"15 years on he is more experienced - I believe that National under Bill English's leadership would win the election in 2017."