Opposition Leader Tony Abbott has indicated a Coalition government could change its position on gay marriage, after state Liberal premiers came out in support of the idea.

New South Wales Premier Barry O'Farrell has voiced his support of same-sex marriage and called for a conscience vote in Federal Parliament.

West Australian Premier Colin Barnett has also backed calls for a conscience vote, although he says he is personally opposed to gay marriage.

Speaking to ABC Radio in Melbourne, Mr Abbott said he did not want the marriage laws to change.

But he said the issue would be a "matter for the post-election party room" if the Coalition won September's federal poll.

"I'm not trying to say that the party is committed forever and a day to the current position," he said.

"I'm saying that this will be a matter for the post-election party room."

On Thursday, New Zealand's parliament passed marriage equality legislation, becoming the first country in the Asia-Pacific region to legalise gay marriage.

But Mr Abbott says that does not mean New Zealand is more progressive than Australia.

"I think it means in this respect that New Zealand is just different," he said.

Liberal frontbencher Christopher Pyne has also said the Liberal party could change its policy on keeping the Marriage Act.

He told Channel Nine the party room would decide on the policy if the Coalition wins government.

"We might well end up with some recognition of same-sex couples," he said.

Family values

Barry O'Farrell says Australia should now catch up with the New Zealanders.

"Let's allow members to have a conscience vote. It was New Zealand that in 1893 first gave votes to women, it took us another nine years to do it," he said.

"It shouldn't have to take us another nine years to [follow] the lead of our cousins across the ditch."

Mr O'Farrell says he supports same-sex marriage "as a Liberal".

''My view - a view that I've come to in recent years - is that as a Liberal who believes that commitment and family units are one of the best ways in which society is organised, I support the concept of same-sex marriage,'' he told Fairfax.

As he arrived at COAG talks today, Mr Barnett told the media he would support a conscience vote on the issue.

"It is a conscience vote for most parliaments. I don't support gay marriage but I acknowledge many Australians are," he said.

"We are probably changing our view as a nation on that."

Tony Abbott, who has a gay sister, has said he originally felt threatened by her sexuality but that has now changed.

Earlier this month two of his daughters said they supported same-sex marriage.