Polls suggest that the contest for the traditionally safe government seat of Selwyn will be a cliff-hanger, following the collapse in support for the main opposition Labour Party and a strong showing by the left-wing Alliance.
'The Alliance started the campaign as a long shot and they are now a near shot,' a political scientist, Keith Jackson, said. But the popular Alliance leader, Jim Anderton, said that even if his party wins - most commentators predict it will lose narrowly - he will favour Mr Bolger's National Party continuing to govern rather than see a snap election.
Before Selwyn's National Party Member of Parliament, Ruth Richardson, resigned last month, the government had 50 seats. Labour had 45 and the Alliance and New Zealand First parties had two each. A win would give the Alliance three seats and prevent Mr Bolger from passing legislation without the Alliance's support.
Mr Anderton, however, says his party will stand by its left-wing manifesto and will oppose such measures as the privatisation of state assets and the deregulation of coastal shipping.
Only the National Party appears to want an early election because the economy is growing robustly.