Political pollsters see no clear leader yet in the race to lead the National Party.

Horizon Research has released an opinion poll of a thousand voters, and of the five candidates running for the leadership, Amy Adams the most public support.

However, amongst people who vote National, Judith Collins comes out on top.

She's also seen the most polarising figures, with more National party voters ranking her dead last than putting her first.

Horizon's Grant McInman says it's a different contest than when Bill English became leader.

"It sort of suggests that the National Party caucus has got a difficult choice. It depends whether your appealing to younger people or people in that middle age group or if you want to appeal to older people."

Other frontrunners are Mark Mitchell, who's popular with younger National voters, and Steven Joyce, whose popularity sits with over-55-year-olds.

McInman says the candidates are each popular with specific sections of the voting population.

"Because Amy Adams has very good appeal, she may morel appeal more to people that might vote National in the future. On the other hand, if you look more closely at who supports the National Party, than she's got less support."