THE Yes campaign has a healthy lead in the marriage equality postal survey, a new poll has found, with just three weeks until voting closes.
A Newspoll, conducted for The Australian, shows that 59 per cent of those who have voted so far ticked the 'Yes' box.
The Australian Bureau of Statistics says 67.5 per cent of eligible voters have mailed in their votes, a turnout far higher than anyone expected.
The Australian reports that support for marriage equality is more popular with young Australians, however only 57 per cent those aged 18 to 34 and 63 per cent among those aged 35 to 49, say they have voted so far.
That compares to 71 per cent of Australians aged 50 to 64 and 74 per cent of those over 65 saying they have posted their surveys.
Of those who have not voted, support for No was only 38 per cent - slightly lower than the support among those who had already voted.
The ABS will stop accepting the envelopes after 6pm on Thursday, November 7. The result will be declared on Wednesday, November 15.
It came as Labor threw its weight behind a private bill drafted by a Liberal senator if the same-sex marriage survey delivers a majority Yes vote.
West Australian senator Dean Smith's bill allows for the change to marriage laws while also protecting religious freedoms.
The Labor caucus yesterday voted to allow a conscience vote on the bill - which is believed to have the best chance of passing parliament - should the survey return a positive result on November 15.