SYDNEY —  Australians voted decisively in favour of allowing same-sex couples to marry, sparking joyous celebrations on Wednesday across the country even though the change must still be enshrined in law.

Thousands of marriage equality supporters took to the streets, dancing and singing when the results were announced, as colourful confetti filled the sky at rallies in cities across the country.

Almost 62 per cent of the 12.7 million people who participated in the two-month non-binding postal survey voted in favour of allowing gay marriage, with Prime Minister Malcolm Turnbull vowing to move a bill in favour of equality by Christmas.

Australians "have spoken in their millions and they have voted overwhelmingly yes for marriage equality," Turnbull told reporters in Canberra.

"They voted yes for fairness, yes for commitment, yes for love."

Nearly 80 per cent of eligible voters took part in the poll, despite fears that many young people might not respond to the postal survey in the digital age.

"This means everything, this means everything," said Chris, at a huge rally in Sydney, fighting back tears and hugging his partner Victor.

The "yes" vote was supported by majorities in every state and territory in the vast and varied nation, according to the Australian Bureau of Statistics, which ran the survey. The "no" vote garnered 38.4 per cent.

"Australians can have confidence these statistics reflect the view of the eligible population," the statistics bureau chief Davis Kalisch said.

Parliament must now adopt legislation to give the result the force of law with Turnbull confident lawmakers would use their "conscience vote", where they are not obliged to vote along party lines, to bring in change.

’So proud’

The result looks set to cap years of political wrangling about the issue that has seen Australia lag behind its international peers in legalising gay marriage.

Irish-born Qantas chief Alan Joyce, who is openly gay and campaigned strongly for the "yes" campaign, also fought back tears as he spoke of his joy.

"I was so proud of Ireland in May 2015 when they became the first nation in the world to vote for marriage equality... But today I am even more proud of Australia, the country of my selection," he said in Sydney.

"No" campaigners congratulated their opponents but vowed to push for religious protections and exemptions.

"In a democracy, just because you win it doesn’t mean you... bulldoze forward," said Senator Eric Abetz, a prominent "no" campaigner.

"Keep in mind there are 4.8 million of our fellow Australians that actually voted no... Do we say they should no longer be heard? Or do we actually ask them questions as to how can their concerns be alleviated so we can move forward as a nation?"

The result is seen as a positive for Turnbull, a moderate who supports marriage equality.

But he must now battle hardliners within his party who want laws that allow commercial service providers to reject same-sex weddings and let parents pull their children from school programmes they feel undermine heterosexual traditions.

Turnbull and the opposition Labor Party have backed a simpler draft bill that legalises gay marriage while allowing religious institutions to refuse to wed same-sex couples if they oppose the practice.

That bill is expected to be introduced in the Senate as early as Thursday.

A survey of federal politicians by the Australian Broadcasting Corporation published on Tuesday found that 72 per cent of the lower House of Representatives would support changes to marriage laws and in the Senate, 69 per cent would approve the changes. — AFP