The ruling Labour Party won 50 seats, one more than the opposition National Party, giving neither side a majority in the new 122-seat parliament. Both parties are scrambling to secure the support of the six minor parties to form a coalition.
The outcome could depend on 218,000 uncounted absentee votes, many from expatriates, which the electoral office will not declare until 1 October under the complex mixed-member proportional voting system.
Miss Clark said she was confident she could form a viable government after fighting the election on her strong economic performance and independent foreign policy. She said: "You are looking at Labour working with a range of small parties to get something sustainable, durable, and can keep New Zealand growing."
She said she wanted to "heal wounds" opened by a pledge from Don Brash, the National Party leader, to cut special programmes for the Maori, who make up 15 per cent of the population of four million.
Mr Brash, a former head of the central bank, nearly doubled the party's vote from 2002 and is refusing to concede defeat until all votes are counted.
He had promised tax cuts and vowed to scrap seven seats reserved for Maori MPs and welfare policies he condemned as "state-sponsored separatism". Mr Brash said during campaigning he would scrap New Zealand's 20-year-old nuclear-free laws if to get a free-trade deal with the US.
Since coming to power in 1999, Miss Clark has presided over a booming economy, helped by strong prices for agricultural exports and a surge in tourism. Unemployment is at a 30-year low.
Without Maori Party support, Mr Brash said a National-led coalition was unlikely. "There are some differences between the Maori Party and the National Party that would seem to be absolutely insuperable."
The Maori Party's co-leader, Tariana Turia, said it would consult supporters to decide who to back.
Midway through Saturday night's vote count a pilot stole a small aircraft and threatened to crash into Auckland's 328 metre-high Sky Tower, the tallest bulding in the southern hemisphere. After 500 people had been evacuated from the tower, the Piper Cherokee crashed into the sea 50 metres off Kohimarama Beach. The pilot, a flying instructor, was taken to Auckland Hospital.