A teenager from Perth, Australia, has turned down an award from her school after she discovered that the MP who sponsored it opposes same-sex marriage.

Grace Gouldstone returned the Ian Goodenough Award, given to students who display a positive attitude and make a special contribution, to Duncraig Senior High School after her discovery.

In a letter to the vice-principal, Stephen Spice, Gouldstone wrote that she felt "strongly that the sponsor of the award, Ian Goodenough MP, does not support the values of that particular award.

"[It] does not reflect the values of our school as a positive and inclusive environment, promoting equality for all. As such, I reject his award."

The 17-year-old said that she was honoured to be the recipient of the award, but couldn't accept it based on the views of the Liberal MP.

Reacting to the rejection, Goodenough said: "I'm OK with that if she feels strongly the other way. Not everybody will agree with me on social issues.

"It's a divisive issue. There are people on both sides of the argument, so there are probably close to half the electorate that think the other way."

Goodenough has came out against same-sex marriage in a vote that has stoked up fierce debate and divided the country.

The Prime Minister Malcolm Turnbull has promised that if the majority of Australians back same-sex marriage, the parliament in Canberra will debate the amendment of the Marriage Act.

Voters have until the 7 November to cast their ballots, with an estimated 75% of all eligible thought to have voted so far.

Results are set to be announced on the 15 November.