Prime Minister John Key says the Government would be willing to work with Labour MP Phil Goff if he becomes Auckland mayor.

The former Labour leader has said he is giving serious thought to running for the city's mayoralty in 2016.

Mr Key said he would "work with whoever becomes the mayor of Auckland".

"Phil Goff has been a very long standing member of Parliament," he said on Paul Henry this morning.

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"It was quite a combative relationship when he was leader of the opposition, but there's no question he had a big work rate and he was a very effective minster."

Mr Key said Maurice Williamson had not yet indicated an intention to run for mayor.

"He hasn't raised the matter with me, he might do, I don't know," Mr Key said.

"In the end, what we did in the last election, and we'll do in this election, we won't endorse anyone. Last time I went to a few fundraisers, for instance for John Banks, so privately I'll do some things where there are other people around and people could work it out, but we won't ultimately go out and say it's this candidate or that candidate."