Almost a quarter of a million people have had their say in early voting ahead of next Saturday's election.

In the first five days of early voting, the Electoral Commission has revealed 308,191 votes have been cast across New Zealand.

It's well up on the early votes cast in previous years - over the same five days in 2014 just 129,816 people voted early, and 51,928 over the same period in 2011.

It's expected as many as 50 percent of voters could have their say before election day.

Counting of early votes will begin at midday on September 23, but results won't be revealed until 7pm.

Labour leader Jacinda Ardern cast her vote early this week and is urging others to vote early to ensure they are enrolled.

Voters can enrol any day before the election, but not the day itself.

Last election 27,000 votes were discounted because those who cast them were not enrolled.

"Our strong message to people is vote early, it leaves nothing to chance. If there's anything wrong with your enrolment details you can fix them at the time," Ms Ardern said.

"I think the only thing that early voting indicates is that people are voting early. I don't think we can read into it for either party and I doubt either of us will."