THE latest same-sex marriage poll shows the Yes campaign is comfortably ahead, with overwhelming support among those who have already voted.

A special Newspoll survey shows a massive 59 per cent of those who have returned their postal ballots are in favour of legalising gay marriage. Just 38 per cent of the millions of Australians who have voted said they were against.

The poll conducted for The Australian comes just a day after the latest estimate from the Australian Bureau of Statistics revealed that 10.8 million survey forms had been returned as of Friday, October 13.

That means around 67.5 per cent of the 16 million forms sent out have been posted back.

The only way in which the No campaign could now succeed is by winning three out of every four remaining votes, according to the figures from Newspoll.

It also found a high level of support for same-sex marriage among those who have not yet voted, with 56 per cent of all respondents in favour of the legislative change and 37 per cent against.

The No side has gained some ground since last year, but not enough to come anywhere near the support for Yes.

Support for same-sex marriage is strongest in the youngest demographic, aged 18-34, with 66 per cent in favour and just 28 per cent against. The ratio narrows as voters get older; people aged over 65 are the only group more likely to vote No, with 49 per cent against legalising gay marriage to 44 per cent in favour.

Older voters are more likely to return their ballots, but it is looking increasingly unlikely they can reverse the trend at this juncture.

Still, the votes continue to stream in, with 800,000 forms returned each week over the past fortnight. The poll found that 65 per cent of respondents had already voted, and just under 20 per cent said they still definitely would.

The figures have defied the expectations of both opponents and proponents of same-sex marriage, who did not predict such a significant voter turnout in a non-compulsory postal ballot.

The Equality Campaign’s Shirleene Robinson said it showed Australians hadn’t forgotten about LGBTI neighbours. “Australians have recognised how important this issue is to their family, friends and colleagues and are doubling down to ensure that when this campaign is over we are left with the fair, equitable and inclusive country that we all want,” she said.

“This is a great result and confirms that Australians want to get this done and are returning their surveys in record numbers.”

And it seems the No side is beginning to accept defeat, with Immigration Minister Peter Dutton, who is against same-sex marriage, telling the audience at a Fairfax media event in Sydney last week he believed Yes would win.

The minister personally opposes changing the law but has pledged to vote for it in Parliament if the Yes campaign is successful.

Treasurer Scott Morrison, who also supports traditional marriage, said he would wait to see the results. “Australians are having their say at the moment. That’s what I wanted them to have,” he told the ABC.

With three weeks left until the survey closes on November 7, many Australians have indicated that they will keep voting right down to the wire. But 50 per cent of Australians who responded to the Newspoll said they opposed the Government undertaking a postal plebiscite at all, to 43 per cent in favour and seven per cent uncommitted.

The ABS has warned all surveys should be posted back by October 27 to ensure they arrive before the deadline.

WHAT YOU NEED TO KNOW

• Requests for replacement forms close on 6pm, October 20. You can also pick up a form from certain locations or call 1800 572 113.

• There’s a paperless option for eligible Australians travelling or living overseas, people in aged care facilities, or those with an illness, injury or disability, to respond online or by phone.

• Survey forms must be received at the ABS by 6pm (local time) on November 7 to be included in the count.

• Survey results will be published on November 15.

• More information is available at www.marriagesurvey.abs.gov.au