Almost 60 per cent of eligible Australians have cast their votes in the same-sex marriage postal survey, but campaigners from both sides of the debate insist the fight is far from over.
The Australian Bureau of Statistics received about 9.2 million ballots by the end of last week, accounting for 57.5 per cent of the forms it sent out.
"We hope that this update will serve as a reminder to those who have not submitted their form to do so promptly if they wish to have their say," deputy statistician Jonathan Palmer said on Tuesday.
The ABS, which published the estimate on Tuesday afternoon, will provide an update every week until the postal survey closes on November 7.
The count is based on Australia Post's assessment of the number of containers of sorted envelopes rather than a count of individual forms.
Marriage equality campaigner Alex Greenwich said research and polling showed a number of young people had filled in their forms but not yet returned them.
"So you have not voted until you have posted your 'yes'," he told reporters in Melbourne.
"Do not leave your survey form in your gym bag or on the kitchen table, put that in the box. This document is too important to help shape our nation as a fairer and more equal place."
The Coalition for Marriage says its campaigners will continue tirelessly until the ballot closes and the final person casts their vote.
"The statistics released today tell us that one-in-two Australians are yet to participate in this survey," marriage equality opponent Lyle Shelton said in a statement.
"We want to make sure everyone has their say. Half of the country is yet to make up its mind - this conversation is still wide open."
The results will be published on November 15.