Hundreds rally in support of gay marriage

About 200 people rallied in central Sydney to show their support for gay marriage laws.

About 200 supporters of gay marriage rallied under rainbow umbrellas in central Sydney as the ACT's same-sex marriage laws are being challenged in the High Court by the government.

The ACT's gay marriage laws were to come into effect formally on November 7, meaning the first marriages could happen from December 7.

But with a High Court challenge from the federal government possibly starting on December 3, they might be struck down before any gay couples marry.

Protester Sean Cook, 40, told AAP it was "internationally embarrassing" that Australia was still debating the issue.

"It's really sad that Australia hasn't caught up with the rest of the Western countries," he said as steady rain fell on the animated crowd gathered at Town Hall.

The ratio of opposition to gay marriage in politics didn't reflect the broader attitude of society, protester John Clark said.

"The politicians are too scared of losing their minority seats in Western Australia and Queensland, where all the rednecks hang around," he told AAP.

Mr Clark added that politicians needed to update their definition of families to better reflect modern Australia.

"There's no such thing as 2.4 kids and a mother and father anymore - a family constitutes a lot of different things," he said.

Both men told AAP that Governor-General Quentin Bryce's public support for gay marriage was "awesome" and "a step in the right direction".

Neither were sure whether "traditionalists" such as Prime Minister Tony Abbott would be swayed by Ms Bryce's comments.

Independent Member for Sydney Alex Greenwich said Ms Bryce's comments were "a watershed moment for the campaign".

"Our highest-ranking official has understood the importance of marriage equality and understood that it's an issue that should be above politics and about love," he told AAP.