Updated

New Zealanders will go to the polls Sept. 20 for a general election.

Prime Minister John Key made the announcement Monday. Under the New Zealand system, the prime minister gets to choose the date for the election, which is held every three years.

Opinion polls indicate that Key's conservative National Party remains the most popular single party and is well placed to win a third term.

However, New Zealand's proportional system dictates that political parties must typically find partner parties to form a majority.

On that basis, a group of liberal parties, led by Labour and the Greens, are hoping to gather enough votes between them to topple Key.

The New Zealand economy has grown strongly over the past six months as the country recovers from the global economic downturn.