National's deputy Paula Bennett may have to fight to keep her job, with the party announcing it will also be voting for its second-in-charge when it elects its leader.

The party's 56-member caucus will vote on its leadership team on the morning of February 27 and will decide both the leader and deputy, whip Jami-Lee Ross has announced.

Five people have announced they are running for the top job but so far Bennett said she was happy to stay in the same role she had under outgoing leader Bill English.

Ross on Tuesday told reporters Ms Bennett had herself asked for a vote on the deputy role last week and any others candidates could self-nominate at the meeting.

The results of the vote would not be made public, he said.

Earlier in the day Ms Bennett told media, as things stood, she was happy to be deputy under any of the five leadership candidates.

She would not comment on who she backed for the job.

Steven Joyce, known as the previous government's "minister for everything", on Tuesday confirmed he is running for the leadership - becoming the fifth person to do so.

Former defence minister Mark Mitchell launched his bid on Monday, while Amy Adams, Simon Bridges and Judith Collins announced their interest last week.

Joyce is the last of the likely candidates to come forward.

English's resignation takes effect on February 27.

There will be a secret ballot, with low-polling contenders dropping out until one has a clear majority.

The party's MPs, including Mr English, have largely been keeping tight-lipped about who they would be voting for, although Mr Joyce said no one yet had the 29 votes needed for an outright win.

- NZ Newswire