Sydney, Sep 10 (IANS): Australian Prime Minister Malcolm Turnbull on Sunday said a "yes" vote in the upcoming same-sex marriage poll was a question of "fairness", the media reported.

Addressing the "New South Wales Liberals and Nationals for Yes" campaign launch here, Turnbull said this change had already happened in many countries around the world, reports the Guardian.

"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.

"This is not a cause that divides along party political lines."

Turnbull was joined by New South Wales Liberals, including the former New South Wales (NSW) premiers Barry O'Farrell and Nick Greiner, former NSW Coalition leaders Kerry Chikarovski, Peter Debnam and John Brogden, as well as Sydney city councillor Christine Forster, who is the sister of the former Prime Minister Tony Abbott.

Forster, who is a lesbian, said she had already set a date for her marriage to her partner, Virginia Edwards, on February 2, 2018, in the British consulate.

All of the speakers described marriage equality as a fundamentally conservative value -- one that they wanted to extend to all loving couples, the Guardian reported.

Rallies in support of same-sex marriage were being held in various cities on Sunday afternoon.

The postal survey forms with the question "Should the law be changed to allow same-sex couples to marry?" will be mailed to voters from this week. They will have the option to tick a "yes" or "no" box.

The result of the survey will be announced on November 15, followed by a vote in Parliament on a private member's bill if there is a majority "yes" result.