Amy Adams announced she was a contender for National's leadership flanked by four supporting MPs, but others are still deciding where their caucus votes will go.

There are so far three candidates to replace Bill English - Adams, Simon Bridges and Judith Collins.

Jonathan Coleman, Steven Joyce and Mark Mitchell are deciding whether to put their names up.

"I'm taking my time," said Todd McClay as he went into a select committee meeting in parliament on Thursday.

"I'm going to take some soundings but I'm not going to do that through the media."

Brett Hudson had a similar attitude.

"There's some way to go before we make a final decision," he said.

"I'm not ruling anyone in or out. Ultimately, this will be about what's good for New Zealand."

Mr English's resignation takes effect on February 27 and the 56-member caucus has to elect a new leader before then.

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

Ms Collins was the first to announce on Wednesday that she was standing for the leadership, followed by Mr Bridges and then Ms Adams, who was the only one to turn up with supporters.