Ian Thorpe: It's not too late to vote yes.

Olympic swimming champion Ian Thorpe says it’s not too late for people to hand in their same-sex marriage postal forms.

While it’s too late to vote by post, Thorpe says there are nine drop-off locations at Australian Bureau of Statistics offices in capital cities across Australia, still accepting forms until 4:30pm on Tuesday.

“If you really want to make your vote count, you still have the opportunity go to an ABS centre and drop off your ballot if you haven’t already,” he told AAP at the Melbourne Cup.

Thorpe says he's reassured by the amount of people who have already voted in the postal survey.

"Considering how many people in Australia have voted for this, it's quite reassuring because we know over recent decades how many people have supported marriage equality," he said.

"We are hoping its an overwhelming positive yes result and it leaves our politicians with no excuse but to get on with it."

As a corporate guest at the Melbourne Cup, Thorpe said he was thrilled to be taking part in a great Australian tradition.