The Electoral Commission are advising New Zealanders to get their completed voting papers into a postbox soon.

The second referendum on the New Zealand flag is only three days away from closing.

Chief Electoral Officer Robert Peden said although it is not too late, voters need to make sure their paper is cleared and postmarked before 7pm Thursday.

"Your best bet is to take it to a PostShop before the close of business on Thursday and put it in the postbox there," he said.

"We want everyone's papers back in time, so please don't leave it till the last minute," says Mr Peden.

Preliminary results will be released after voting closes on Thursday March 24, and official results on March 30.

As of yesterday, 1,901,599 voting papers had been received by the Electoral Commission.