Bill English is set to replace John Key as Prime Minister, after the only other contenders dropped out of the race for the National Party's leadership today.

Photo: AFP

Mr English already had enough caucus support, and now has no other competition for the role after Judith Collins and Jonathan Coleman conceded defeat.

He told Checkpoint with John Campbell he was "very happy to be the only candidate, but I'm not a prime minister".

Speaking to reporters soon after Dr Coleman conceded, he said the caucus still had to formally meet on Monday before his leadership would be confirmed, and the question of who would serve as Deputy Prime Minister would have to wait until then.

"I only get to be the leader of the National Party - and therefore the Prime Minister - when the National Party MPs confirm that.

"At the moment they are engaged in sorting out the leadership team, that still has some way to go, and the plan at the moment is that the confirmation of the leadership team will be on Monday, not today," Mr English said.

And a new PM emerges pic.twitter.com/r26yYEfkLu — Richard Bicknell (@dickbicknell) December 8, 2016

Mr English paid tribute to the other leadership challengers.

"I want to thank Jonathan Coleman and Judith Collins for helping the caucus with a constructive discussion about the transition from the John Key-led government.

"John was a strong and positive influence on the caucus and it's been great to have the opportunity to talk through how the National Party caucus wants to reset government."

Mr English said he would not be endorsing a candidate for Deputy Prime Minister at this point, and would not be drawn on the timing of next year's election.

Watch RNZ's political editor Jane Patterson's take on today's developments:

Paula Bennett and Simon Bridges are running for deputy leader and many National MPs say they are still undecided as to who they will vote for.

This morning Mr English said he would give Steven Joyce the finance portfolio if he won the party's leadership.

At a media stand-up earlier this afternoon, Dr Coleman said he could see the way the numbers were going.

"I have just been up to congratulate the next Prime Minister of New Zealand, Bill English. We had a really good chat, and I think he is going to make a very fine Prime Minister of New Zealand. I am going to be supporting him 100 percent because it's absolutely vital that the party comes together, gets on with the job of winning the next election - which I believe we will win - and then supports Bill as Prime Minster through a fourth term and then beyond that."

Congrats .@honbillenglish our next Prime Minister. You're going to make a great PM & the whole team & I are behind you 100% to win in 2017 — Jonathan Coleman (@jcolemanmp) December 8, 2016

Ms Collins, who withdrew from the race earlier this afternoon, also declared her support for Mr English.

Thirty National MPs have publicly stated their support for Mr English, which would be enough to secure him the role.

Ms Collins said it had been good to have the caucus have a say in the process, but she acknowledged Mr English had the numbers.

"It is clear to me that 50 percent of caucus support Bill English as the leader and therefore, as far as I'm concerned, he has won. So with 50 percent of the caucus, I would like to say to my supporters that we should get in behind Bill as the leader."

Mr Key was among those to have publicly backed Mr English for the top job.

Judith Collins says Bill English will be next PM. She will back him. pic.twitter.com/qH9v77NBYO — Mei Heron (@meiheron) December 8, 2016

The new prime minister will be sworn in on Tuesday.

National MPs who have declared support for Bill English:

John Key, Michael Woodhouse, Nathan Guy, Nick Smith, Hekia Parata, Nikki Kaye, Anne Tolley, Louise Upston, Nuk Korako, Chester Borrows, Paul Foster-Bell, Paula Bennett, Simon Bridges, Murray McCully, Jacqui Dean, Todd Muller, Brett Hudson, Jami-Lee Ross, Chris Bishop, Sarah Dowie, Jonathan Young, Todd Barclay, Amy Adams, Mark Mitchell, Jono Naylor, Barbara Kuriger, Jo Hayes, Judith Collins, Jo Goodhew