Two bills calling for the legalization of gay marriage were introduced to Australia's parliament on Monday in a move campaigners said would add momentum to the push for equality.

The private member's bills, introduced by left-leaning Greens lawmaker Adam Bandt and Stephen Jones from the ruling Labor party, take to three the pieces of legislation now before the parliament calling for gay marriage rights.

Greens Senator Sarah Hanson-Young brought a similar bill in the upper house in September 2010 which is now being examined by a legislative inquiry.

None of the bills have enough support to pass into law but rights campaigners said their introduction, which follows Labor's reversal of its official policy to pro-gay marriage in December, showed the tide was turning.

"The Jones bill demonstrates the immense momentum behind reform," said Alex Greenwich, convenor of the Australian Marriage Equality lobby group.

"Three months ago the Labor Party was officially opposed to reform and now we have a Labor member leading the way towards equality."

He described Monday's events as a "milestone on the road to equality".

Greenwich said rights advocates wanted both Jones and Bandt's bills to be examined by the Senate committee looking into Hanson-Young's bill so that "the best possible legislation can be developed and put forward".

Jones said there would not be a debate or vote for some months yet.

In Australia marriage is mandated by federal legislation, so although civil same-sex unions are recognized in five states, the couples are not seen as "married" by the federal government.

All the same, same-sex couples have equal rights with heterosexual couples in areas such as pension schemes and medical benefits.

Until December there had been bipartisan opposition to same-sex marriage in Australia and though Labor's official platform has changed, the party agreed to vote on conscience rather than en bloc, meaning there is presently little prospect of legal change.

Prime Minister Julia Gillard opposes gay marriage, and the conservative Liberal-National coalition has made clear that its members will be expected to uphold the current heterosexual definition of marriage if a vote is called.

"Our position is clear. We believe that a marriage is between a man and a woman and that's the way the Coalition will be voting," said Liberal front-bencher Joe Hockey.