More than three quarters of eligible Australians have partaken in the Turnbull government's same-sex marriage survey, with less than one week left to return forms.
The Australian Bureau of Statistics, which is executing the survey, said it had received an estimated 12.3 million survey responses as of Friday - or about 77 per cent of the 16 million eligible voters.
That puts the turnout well in excess of the 56 per cent who voted in the last US Presidential election, the 61 per cent who partook in Ireland's same-sex marriage referendum and the 72 per cent who cast votes in the Brexit poll.
About 400,000 forms were received in the week leading up to Friday. Although the "yes" campaign took its foot off the pedal last week, issuing a final reminder for voters to post their forms, the survey remains open until 6pm on November 7.
On Tuesday the ABS warned voters to get their forms in the mail "immediately" to meet that deadline. Alternatively, voters can drop off their forms at the Bureau's office in each capital city and in Geelong, during business hours.
The Equality Campaign heralded the "phenomenal" turnout figure, with executive director Tiernan Brady declaring it showed Australians were "passionate about getting marriage equality done".
"No" campaign spokesman Lyle Shelton marked the occasion by releasing a blog post promising that "win or lose the marriage plebiscite, the fight must go on".
He said his "battle hardened" army of volunteers would use its networks and technology formed during the campaign to fight numerous other changes to social, family and educational policies.
"We'll have a rest when the result is announced. But we'll be back," Mr Shelton said.
Acting Prime Minister Julie Bishop on Monday said she believed the "yes" campaign would be successful, as attention turns to the legislation that would follow such a vote.
Coalition conservatives have positioned themselves to attack a draft bill by Liberal senator Dean Smith, which they say fails to adequately protect freedoms of religion and conscience for those opposed to same-sex marriage.
The Turnbull government is anxious to dispose of the issue by the end of the year, although it now faces the additional challenge of a byelection in New England. However, Prime Minister Malcolm Turnbull has said his legislative agenda will proceed unchanged.
Labor has swung its support behind Senator Smith's bill, providing a clear pathway for that legislation to succeed in both chambers.
Polls before and during the campaign have shown a clear lead for the "yes" side, although opponents of change have appealed to what they call the "silent majority" they believe will rally in support of the status quo.
Some polls have indicated a lower turnout among younger voters, however the ABS has not released any official breakdown of participation by age bracket.
