Manukau Mayor Len Brown announced yesterday he would be joining Auckland City Mayor John Banks in the mayoral race.
Mr Key said there was likely to be an "interesting scrap" between Mr Brown and Mr Banks.
He expected more people would put their names forward.
"I think you're going to see quality people putting their name forward; Len's a very quality candidate," he told TV One's Breakfast programme.
"I think it's going to be a great job to be mayor of Auckland, I personally don't want it, but I'm sure there'll be plenty of others who do."
Mr Brown has said he wants Maori seats on the new council despite the Government having ruled them out.
Mr Key said the council could make a local decision on Maori seats and "that's the way it should be".
"Len Brown's effectively campaigning on that, assuming he would happen to get the majority of council to agree with him, but provided he did that then those Maori seats would be in place."
Mr Brown said he wanted Maori seats because "the mana whenua have an increasing business presence within our city, and we need to inspire our young Maori to excel".
"I want to sit around the table with Maori and I want Maori around the table, so for me, there is a lot of work and discussions to be had."
