'No' campaign gaining ground in Aussie same-sex marriage vote

Opposition to same-sex marriage appears to be growing in Australia, two weeks into the two-month postal vote on the issue.

A new The Australian-Newspoll poll has found support slipping to 57 percent, down from 63 percent in August. The 'no' vote is up to 34 percent, rising from 30 percent in August.

Nine percent said they were unsure.

Labor leader Bill Shorten said he expected the 'yes' vote to prevail, despite the fall.

"We all know the survey is an amazing waste of money," he told Sky News. "The fact that we've got a Newspoll survey telling us what we're going to spend $120 million to find out really highlights the futility of it."

The vote isn't binding, and though Australian Prime Minister Malcolm Turnbull backs a change, not all of his MPs do - most notably former Prime Minister Tony Abbott.

Around 15 percent of voters have had their say so far, with turnout expected around the 70 percent mark.

It's been a controversial process, with accusations of ballot-stuffing, homophobic slurs and violence against MPs.

Last week one voter's form had a barcode containing the phrase 'BUMSEX'.