An angry bride has told an anti-same-sex marriage rally to move from outside the front of the Sydney cathedral where the wedding was being held.

A crowd of about 500 people gathered outside St Mary's Cathedral on Saturday afternoon, preparing to march through the CBD, where they chanted "Aussie Aussie Aussie, No No No".

The couple said they had "no idea" the event was going to clash with their nuptials.

"I'd prefer they just moved, to be honest," the bride said.

The couple leave Sydney's St Mary's Cathedral after their wedding. ( ABC News )

Earlier in the day, more than 5,000 people had gathered at Belmore Park, near Central Station, to voice their support for same-sex marriage and march into the inner-west.

Saturday's marches did not intersect, and were held at different times in the afternoon.

No rally organiser Phillipa Bruce said she was expecting a bigger crowd but had some problems when advertising the event.

"Unfortunately, we had radio advertising ready to go out and that was delayed for whatever reason," she said.

"We were expecting a bigger turnout but without being able to reach through the media that's very difficult.

"When your ad gets canned again and again you have to ask questions about what is happening there."

The anti-same sex marriage protest can be seen outside Sydney's St Mary's Cathedral. ( ABC News )

Rival 'yes' rally also held

Deputy Opposition Leader Tanya Plibersek told the Yes rally the survey should never have happened.

"This conflict never needed to be in people's families or in people's lounge rooms, it never needed to be in our community," she said.

"My constituents have had their homes graffitied, spray painted, hateful messages scratched into the walls of their homes.

"$122 million wasted, it never needed to be, so I feel angry as well as sad."

These costumes provided a splash of colour at the Yes rally. ( ABC News: Liv Casben )

The march finished with a dance party at Camperdown, in the inner-west.

The Australian Bureau of Statistics (ABS) this week estimated 10.8 million Australians — or 67.5 per cent of eligible voters — had returned their forms.

With less than three weeks before the final cut off for votes on November 7, those numbers mean about 5 million people are yet to vote.

The Equality Campaign also held rallies in Brisbane and Alice Springs on Saturday.