Labour Party leader Ardern, 40, and National Party chief Collins, 61, are the faces of the election to form the country’s 53rd parliament, a pandemic-focused referendum on Ardern’s three-year term.
Doors to the polling booths opened at 9am local time on Saturday (20:00 GMT on Friday), though a record number of voters had already cast their ballots in advance.
Restrictions are in place on what news media can report about the race until polls close at 7pm (06:00 GMT), after which the Electoral Commission is expected to begin releasing preliminary results.
More than 1.7 million ballots had already been cast as of Friday, accounting for almost half of the about 3.5 million New Zealanders on the electoral rolls.
The election was originally set for September 19 but was delayed by a virus outbreak in Auckland that has now been contained.
A survey that came out on Friday ahead of the polls showed that support for Ardern’s party has dropped, but it would still be enough for her to govern alone.
The Newshub-Reid research poll showed support for Ardern’s party at 45.8 percent, down 4.3 percentage points from the last poll. The opposition National Party was at 31.1 percent, up 1.5 percentage points.
Meanwhile, special votes, including ballots from New Zealanders overseas and those who vote outside their home constituencies, will only be released on November 6.
New Zealanders are also voting on referendums to legalise euthanasia and recreational marijuana. The latter vote could make New Zealand only the third country in the world to allow the adult use and sale of cannabis nationwide, after Uruguay and Canada.
Results of the referendums will be announced on October 30.
New Zealand switched to a mixed-member proportional system in 1996 in which a party or coalition needs 61 of Parliament’s 120 seats – usually about 48 percent of the vote – to form a government.
This means minor parties often play an influential role in determining which major party governs. (Aljazeera)