Malcolm Turnbull has made his strongest case yet for voters to support the Yes vote in the same-sex marriage postal survey.
The prime minister, who has previously said he supports same-sex marriage, on Sunday made his strongest yet statement pressing the case for the yes vote.
"Fundamentally this is a question of fairness," he told the Sydney launch of the NSW Liberals and Nationals for Yes.
He said he was "utterly unpersuaded" by the idea that his 38-year-long marriage to wife Lucy was undermined by gay couples.
"The threat to marriage is not gay couples, it is a lack of loving commitment," he said.
He noted other countries where same-sex marriage had been legalised.
"In any one of those nations has the sky fallen in, has life as we know it ground to a halt, has traditional marriage been undermined and the answer is plainly no," he said.
Tens of thousands of same-sex marriage supporters rallied in Sydney and Brisbane on Sunday.
Opposition Leader Bill Shorten told the Sydney rally it was time for same-sex marriage and apologised that politicians had failed to make it happen.
"I'm sorry that the parliament has not already resolved this matter," Mr Shorten said.
"I'm sorry for all of the hurtful and stupid things which have been said and are going to be said until we win marriage equality."
The survey forms with the question "Should the law be changed to allow same-sex couples to marry?" will be mailed to voters from this Tuesday.
They'll have the option to tick a "yes" or "no" box and the result will be announced on November 15.
Mr Turnbull said if the majority of Australians voted yes like him, a private member's bill would be presented which he predicted would "sail through the parliament".