Same-sex marriage postal survey: 'Love has had a landslide victory' as 'Yes' wins

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LIVE: Same-sex marriage vote results and live coverage

Australians have emphatically voted in favour of legalising same-sex marriage, saying "yes" to the historic social change by a substantial margin of 61.6 per cent to 38.4 per cent.

After years of political stagnation, the public has now tasked the Turnbull government with changing the law before Christmas to allow same-sex couples to marry.

Almost 80 per cent of eligible voters participated in the unprecedented voluntary postal survey, giving the verdict an authority unmatched by most elections globally.

It means Australia is poised to join 25 other countries that have granted marriage equality to gay couples, including the US, Canada, New Zealand and the United Kingdom.

At street parties across the country, gay and lesbian Australians cheered, danced and embraced as the results were announced by the chief statistician on Wednesday.

It is a landmark moment in Australia's mixed civil rights record: it was one of the first countries to give women the vote, but still struggles with Indigenous reconciliation and is one of the last English-speaking democracies to legalise same-sex marriage.

The result is also a significant victory for Prime Minister Malcolm Turnbull, of the ruling centre-right Coalition, who is a longstanding supporter of same-sex marriage and firmly believed the "yes" vote would prevail.

"Love has had a landslide victory," declared Alex Greenwich, co-chair of the Equality Campaign, from a public gathering in Sydney, where John Paul Young's classic "Love Is In The Air" was played.

"Getting to this point has not been easy, but rarely in your life can you celebrate with such pride overcoming adversity to make history."

Mr Greenwich said the campaign's support and momentum had exceeded all expectations, and the result had delivered "an unequivocal mandate" for politicians to vote through the change by the end of the year.

Every state and territory voted "yes" by more than 60 per cent except for NSW, where the "yes" vote was 57.8 per cent, and the "no" vote was 42.2 per cent.

The ACT had the highest "yes" vote in the country at 74 per cent, followed by Victoria at 64.9 per cent.

Participation in the survey exceeded 70 per cent across all age groups, including younger voters. Almost 80 per cent of 18 and 19-year-olds voted, the ABS revealed, with the lowest turnout (71.9 per cent) among 25 to 29-year-olds.

Mr Turnbull, speaking shortly after the results were announced, heralded the "overwhelming" support Australians had expressed for same-sex marriage.

"They voted 'yes' for fairness, commitment, love," he said. "It is unequivocal, it is overwhelming."

"And now it is up to us, here in the Parliament of Australia, to get on with it - to get on with the job the Australian people have tasked us to do, and get this done this year, before Christmas. That must be our commitment."