Prime Minister John Key is predicting a "tight and tough" election with the Government up against a "left wing block" of parties.

Mr Key told more than 250 party faithful at a conference in Hamilton today National could not be lulled into a false sense of security by high polling numbers ahead of the September 20 general election.

He said National was not just up against the lower polling Labour but its left counterparts including the Greens, New Zealand First, and Mana.

"The real risk for us is to underestimate just how close this election will be.


"None of us should be deluded into believing that a big poll lead by National against Labour means we have election 2014 in the bag."

He said if the public sensed it would not be a change of Government election, that could translate to a lower voter turnout which could swing the result in favour of the opposition.

Labour suffered its worst defeat in years at the last election he said, but National still only just kept power because it was not a First Past the Post race.

Mr Key said the party had to work hard to keep voters interested and the Government would begin making policy announcements soon.