Key Points:

National leader John Key has warned New Zealanders against a "five-headed monster" of a Labour-led government.

Speaking to reporters in Greymouth this morning, Mr Key said voters should be wary of a coalition government that could include Labour, the Progressives, the Greens, New Zealand First and the Maori Party.

"Do [New Zealanders] want to put in a National government with a fresh view that will work going in one direction with a small group of parties, or do they want a potentially five-headed monster?" he said.

His comments come in the wake of a TV3 poll, which last night showed a Labour-led coalition with support from the Green Party, the Maori Party and the Progressive Party could govern.

The latest Herald-DigiPoll survey, the results of which were released today, found Labour's polling had improved slightly, but not enough to dent National's commanding election-race lead.

Mr Key said a "Helen Clark-led government cobbled together with all sorts of different parties" with "competing interests" would not be in the best interests of New Zealand during a period of "difficult economic times to manage".

He said a coalition such as that proposed by the TV3 poll could see six or seven leaders in government, given that the Maori and Green parties have co-leaders.

Prime Minister Helen Clark says Mr Key's comments show he is a bit rattled.

She says they are ridiculous, as the National leader is trying to stitch up a government involving Act, United Future and the Maori Party.

"He knows that any arrangement from National that brings Roger Douglas anywhere near government is something that people do not want at all.

"So he's trying to cover that very unpopular fact."

Helen Clark maintains Labour has a real chance of forming the next government, if it can encourage people to vote.

- with Newstalk ZB