"To be sure that your voting paper gets back in time to be counted, you should take it to a PostShop before the close of business on Friday and put it in the post box there.
"We want all voters to have their voices heard and votes counted, so don't leave it until the last minute."
In the referendum, voters were asked to rank five flag designs selected through the flag consideration process. They can rank as many or as few as they wish.
Another referendum in March will choose between the most preferred option from the first referendum and the current flag. The flag that receives the most votes in the second referendum will be the official flag of New Zealand.
• For more information about voting in the referendum, call 0800 36 76 56 or visit www.elections.org.nz/flag.