Act Party leader David Seymour says being Deputy Prime Minister isn't out of the question - but it's unlikely.

During last night's second leaders' debate, National's Judith Collins said he'd be excellent in the role if her party won the election.

Seymour told Kerre McIvor it's not on his mind.

"Act has always been more focused on policies and what we can leave behind to make this a better place, than any particular job".

He says John Key offered him the opportunity to be a minister in the past, which he turned down.

"I thought, look there's the limo, a pay rise, the title and everything else but at the end of the day, there are lots of people who've been ministers and they can't point to something they've done for New Zealand".

"I'm really proud we got End of Life Choice across the line by me turning down being a minister and I'm pretty prepared to make that sort of decision again".

Seymour's meteoric rise in the 1News/Colmar Brunton poll this week put Act up to 8 per cent, 1 per cent above the Greens. It means the party would secure 10 seats in Parliament.

From a one-man band to potentially bringing nine other MPs back to Parliament with him, it could mean the biggest caucus for Act since 2002, when it had nine MPs under leader Richard Prebble.

Seymour is live on NewstalkZB with Kerre McIvor for an hour from 10.07am.

Seymour himself was at 2 per cent as preferred Prime Minister, ahead of Winston Peters' 2 per cent in the TVNZ poll.

National leader Judith Collins said this morning she'd have no problem appointing Seymour as Deputy PM should a National-Act alliance hit the 51 per cent party-vote mark on election day.

Collins told Mike Hosking this morning she thought Seymour would make an "excellent" Deputy Prime Minister in her government which was met with a "jeepers" from Jacinda Ardern during last night's MediaWorks leaders debate.

"David Seymour is a principled person in my experience and he and I have worked together before. I'd rather have him any day than what Miss Ardern has had," Collins said.

Sunday's Newshub Reid Research poll put Act up three points to 6.3, which would give the party eight seats in Parliament.

The stars have aligned for the party that's battled through successive leaders and scandals, to now be polling as the third-largest party behind National.

In the past the focus on Act, come election time, has been whether or not it would get the nod from National in Epsom - the electorate seat that's been the party's lifeline for a number of election cycles.

Seymour now mounts the argument he's able to secure that seat under his own steam.

Not only that, but Act, as one of the smaller parties, has been polling over the 5 per cent threshold in recent months, meaning the Epsom seat is a "good to have" for Seymour, but not as crucial for the party's survival.

The combination of Seymour's consistent and persistent campaign on the End of Life Choice Act, his sole opposition to the first tranche of firearms reforms and the woes of political ally National, mean Act is sitting pretty for the first time in two decades.

- Additional reporting, Jo Moir RNZ