Australians are being advised to send in their completed marriage-law postal survey by 6pm Friday to make sure it reaches the Australian Bureau of Statistics before voting closes on November 7.

An estimated 11.9 million votes have been received by the ABS as of October 20. That means nearly 75 per cent of enrolled people have mailed their survey forms already.

But last week’s Newspoll showed young people were least likely to have voted so far.

Only 57 per cent of 18- to 34-year-olds surveyed by Newspoll had voted, compared with 63 per cent of 35- to 49-year-olds, while 71 per cent of 50- to 64-year-olds and 74 per cent of those aged 65 or older are believed to have returned their ballots.

Two-thirds of young people support same-sex marriage, a figure the Equality Campaign is keen to increase to ensure a “Yes” vote comes out on top.

Equality Campaign spokesperson Clint McGilvray told Broadsheet, “Our job at the moment is to encourage anyone who hasn’t posted their vote to get theirs in the postbox. We’re encouraging everyone, particularly young Australians, to make sure they don’t miss out on their opportunity.”

If you are yet to receive your survey form, it is now too late to request it.

Survey results and final participation rates will be published on November 15.