John Key tours roading projects with aspiring deputy Simon Bridges

The outgoing Prime Minister is this morning touring roading projects with one of the two National MPs who have put their hand up for the deputy Prime Minister role.

But he would not say who he is backing for the deputy role.

In one of his last commitments as the country's leader, John Key was with Transport Minister Simon Bridges in Auckland's northwest to mark the start of construction on a long-sought intersection upgrade.

A new roundabout in the township of Waimauku will replace the current intersection on State Highway 16 and Muriwai Rd, making it safer for all road users including pedestrians and cyclists.

Key also accompanied Bridges in Warkworth this morning to mark the start of construction of the Puhoi to Warkworth motorway.

On his arrival at the sod-turning for the Puhoi to Warkworth motorway extension Key would not say who he is backing for the deputy role.

Key said the cool thing was they were both outstanding candidates. He said he would "let you know on Monday afternoon" who he voted for.

At the ceremony Bridges said it was going to be a tough contest. "I'm feeling pretty good, there is a good sense of momentum," he said.

Bridges reiterated the need for rejuvenation within National, saying the party had huge strength in the base and experience that is there, but balancing that is a need for change and revitalisation.

Bridges said the level of support English is getting at the moment is "decisive" with a strong number of ministers and backbencher coming out in support of him.

"It would be very hard to go past one of his strengths of the stabilising force that he is.

"What is clear is this isn't going to be a John Key government. It has got to be a Bill English government and I want to be helping with that to ensure it does have its own flavour and change to it," Bridges said.

Asked what portfolios he would like in an English-led cabinet, Bridges said he had a few ideas at the different end of the spectrum from a history in economic growth, including transport, to the social sector, where he has not had a portfolio.

He would not say which ministers he believe should go, saying that would be a matter for the new Prime Minister.

Key announced on Monday he would resign as the country's leader and said he endorsed Finance Minister Bill English to replace him. A decision on the new Prime Minister is expected by Monday.

Bridges put his name forward for the deputy Prime Minister role yesterday.

He is going up against Social Housing Minister Paula Bennett.

Bridges said he had not "formally done the numbers" to gauge support for his bid but feels there is strong support for his candidacy.

"I have spoken to a whole raft of colleagues, and that has been influential in my decision. I wouldn't like to put a number on it but I feel good support and a sense of momentum about my candidacy."

Rodney MP Mark Mitchell likened the leadership contest to speed dating or Tinder.

"It's really important that the candidates get around caucus ," said Mitchell, who noted it had been a long time since a change in the party leadership.

"Two-thirds of our caucus have never been through a process like this. We are very lucky in that we have a very democratic process in how we run our selections in the electorates and really we have put together a process very similar to that," he said.

Mitchell, one of several backbenchers knocking on the door for a Cabinet post, said it was recognised that a bit of rejuvenation and a refresh was a good thing.

"The Prime Minister has been very good at doing that and it has been signalled that it will carry on," said Mitchell, who is backing Bill English for leader but undecided on who to back for deputy.