A last-minute surge has seen a record number of Australians enrolled to vote ahead of the upcoming postal survey on same-sex marriage.
The Australian Electoral Commission released figures it described as "extraordinary" on Friday, showing 90,000 new voters - mostly the young - had joined the roll since the survey was announced on August 8.
The development delighted same-sex marriage advocates but alarmed nervous Coalition MPs, who believe the enlarged youth vote will come back to bite them at the next election.
A further 675,000 people had updated their electoral details, and 165,000 transactions were yet to be processed as of Thursday night, the AEC said. In total, almost 1 million Australians had either enrolled for the first time or updated their details.
Once all transactions are processed, the number of new voters should easily exceed 100,000. Electoral Commissioner Tim Rogers said he expected the total proportion of Australians on the roll, which was 95.3 per cent on July 31, to reach a "record high" once processing was completed.
"The maintenance of the roll is a significant achievement given the trend throughout recent electoral cycles for enrolment rates to dip mid-cycle," he said.
The result is notable because it has only been 14 months since the last general election. By comparison, 132,000 new voters enrolled in the lead-up to the July poll.
Same-sex marriage advocates were elated at the news on Friday, following a two-week recruitment drive to ensure young, progressive Australians were correctly enrolled to vote.
By Tuesday night, almost 55,000 new voters had joined the roll. That means a further 35,000 had their enrolments processed in the 48 hours before the roll closed on Thursday night.
Equality Campaign executive director Tiernan Brady, who had predicted a "late surge", said the result reflected "the most successful enrolment campaign in the history of federation".
"This was about people not being complacent," he said. "People aren't going to sit back - they're going to stand up for their friends."
Mr Brady, who ran the campaign for same-sex marriage in Ireland, was due to address about 500 supporters in Fremantle on Friday night to kick off the "yes" campaign.
Meanwhile, Australia's most prominent gay businessman, Qantas chief executive Alan Joyce, pledged to donate "a significant amount" to the campaign's coffers.
"I personally will be donating money to the campaign, a significant amount, because I'm passionate about it," he told reporters on Friday.
"I'll be spending as much time as the campaign wants me to speak[ing] about the cause and why this is important."
While the massive rise in new voters has buoyed the "yes" campaign, it has disturbed some Liberals who fear the government has shot itself in the foot by fostering a process that has encouraged young, progressive voters to enrol.
One Liberal MP said conservatives were particularly shocked by the success of the enrolment drive, but argued they should not be.
"This was always going to happen. They wanted their plebiscite, they should have been able to foresee this," the Liberal MP said.
"Young people care more about same-sex marriage than they do about elections. They're more interested in whether their friends can get married than choosing between Malcolm Turnbull and Bill Shorten."
Peter Phelps, a Liberal member of the NSW Parliament, tweeted: "So an extra 90,000 people to vote against Coalition in a general election following the [High Court] handing down its inevitable s44 ruling? #genius."
Earlier this week a conservative government minister said he was relaxed because young people "would have enrolled in the lead-up to the next election anyway" and "they'll turn into Liberal voters eventually".
The electoral roll closed on Thursday night. Unless a High Court challenge to the legality of the postal survey is successful, the Australian Bureau of Statistics will mail out survey forms starting September 12.