English is running as the candidate of trust and stability; Coleman is running as a new-generation candidate who would bring fresh blood to the Cabinet, and Collins is running as the toughest of them all.
Amy Adams and Simon Bridges have ruled themselves out of contention for the leadership. Paula Bennett has not but sources say she is not likely to stand.
Many caucus members have not made up their minds.
Almost all who have publicly declared any preference are Cabinet ministers backing Finance Minister and Deputy Prime Minister Bill English. Ministers Anne Tolley, Hekia Parata, Louise Upston, Michael Woodhouse, Nathan Guy and Nick Smith have thrown their weight behind English, as has outgoing Prime Minister John Key.
Minister Nikki Kaye, who has been on leave for cancer treatment, came back yesterday for the caucus meeting. She has also weighed in behind English and said she would stand again in Auckland Central.
Christchurch-based list MP Nuk Korako, one of the few backbenchers to declare, has also backed English.
Coleman is making a strong pitch to the backbenchers, many of whom have not made up their minds but want a contest.
Some backbenchers who want change say they could be satisfied with English if he committed to rejuvenation through a major Cabinet reshuffle. That would mean cleaning out so-called "deadwood", which could lead to disunity.
The three most likely contenders for deputy are Bennett, Bridges and Adams. It is not yet known whether any of the contenders will state their preferred deputy until after the leadership vote next Monday.
But sources said formal tickets were unlikely because the caucus wanted the right to elect the deputy.
The possibility of Coleman or Collins becoming deputy to English should they muster a very good showing in the leadership contest cannot be completely discounted.
Their bids are also seen as setting themselves up for a strong run in a year if English wins the leadership now but National cannot win a fourth term.
Key attended caucus yesterday morning to explain his decision to resign but left before discussion on how he would be replaced.
Coleman declared first, then English then Collins.
English said the circumstances were different now to when he led the party to its worst defeat in 2002.
Back then he was 39 and had six children aged under 13. Now his youngest child was 17 and he was in a position to be more focused.
He acknowledged that leadership contests could be divisive but he said the caucus understood the importance of cohesion and stability. "Unity is everything in this business."
Collins said next year's election campaign would be the toughest one National had ever fought and it needed some of the toughest people to run it.
She also said she was "utterly authentic. I'm going to say exactly what I think and I'm going to call it as I see it."
Coleman said it was clear there was an appetite in the caucus for a contest. It was time to build on the gains of the eight years under Key.
"I feel that it needs generational change. It is going to need new thinking in policy areas.
"It is going to mean new personnel so combining the best of the current line-up with those who are coming through the caucus."
Nominations will remain open until the vote at a special caucus next Monday.
Bill English, Deputy Prime Minister, Finance Minister, Housing New Zealand
• Raised in small Southland town of Lumsden, head boy at Silverstream College, studied commerce and English literature at Otago University, worked as farmer and Treasury analyst.
• Conservative Roman Catholic who has opposed same-sex marriage, abortion, euthanasia and the decriminalisation of prostitution.
• Lead National to its worst election result (20.9 per cent) in 2002, and later said he would never lead the party again.
• Has produced eight budgets as Finance Minister, including tax cuts in 2010 and the first rise in welfare payments in 43 years last year.
• Married to Mary and has six children.
Jonathan Coleman, Health Minister and Sport and Recreation Minister
• Raised in Meadowbank, Auckland, by his mother after father died when he was 11.
• Auckland Grammar head boy, later studied medicine in Auckland and business in London, worked as a GP in Otara.
• As Defence Minister, led New Zealand's withdrawal from Afghanistan in 2012. The first doctor in 70 years to become Health Minister.
• As National's health spokesman, was once accused of blowing cigar smoke in a woman's face in a British American Tobacco corporate box at a U2 concert.
• Married to Sandra and has two children.
Judith Collins, Corrections Minister and Police Minister
• The youngest of six children, she was raised in a dairy farming family in Hamilton.
• Worked as a lawyer for 10 years before Parliament, and once owned a restaurant in Takapuna. Initially supported Labour but switched to National.
• Famously tough politician who has made bail laws stricter, introduced Tasers for police, and earned the nickname "Crusher" for her policy of destroying boy racers' cars. Also led reforms of ACC and alcohol laws.
• Involved in several controversies, including an allegation she tried to undermine the head of the Serious Fraud Office when she was Police Minister.
• Married to David Wong-Tung and has one son.
