Melbourne Gay Pride parade today march today held in St Kilda. Image shows Tony Abbott's lesbian sister, Christine Forster (right) with her partner Virginia Edwards. Photo by James Boddington. Sunday Febuary 1 2014

Christine Forster (right) with her partner Virginia Edwards. Photo: James Boddington

Prime Minister Tony Abbott's sister Christine Forster is determined to marry her fiancee Virginia Edwards in Australia, but concedes she likely faces a ''long engagement''.

Sporting a rainbow tie-dye T-shirt and with her partner by her side, Ms Forster marched with fellow Liberal Party politicians in the Pride March on Sunday.

About 30,000 people braved near-40-degree heat to watch the march on Fitzroy Street, St Kilda.

Ms Forster, a Liberal City of Sydney councillor, said the march was a ''wonderful celebration of community, diversity and equality''.

She said Australia's laws preventing same-sex marriage were ''the last bastion of inequality for gay and lesbian couples''.

Ms Forster said she and Ms Edwards had agreed to only get married in Australia.

''It's not a pressing need for everyone, but for same-sex couples wanting to get married it is extraordinarily pressing,'' she said.

She said marriage equality was now ''open for discussion'' within the Liberal Party. ''That's a big shift in my mind.''

Pride March Victoria president Matt Renwick said the march was a celebration.

''We are a strong and dynamic community - there is something for everyone,'' he said.

''We are here and we are proud.''