A carbon tax battle has spilt onto the streets of Melbourne with those in support of a price on carbon claiming victory.

Outside Prime Minister Julia Gillard's electorate office in Werribee on Saturday, 400 protesters gathered with Liberal Victorian senators Mitch Fifield and Scott Ryan to protest against the federal government's plan to put a price on carbon.

Meanwhile, at Treasury Place in Melbourne's CBD, an estimated 8000 protesters gathered to support the prime minister's carbon tax plan and call for action on climate change.

Paul Mackay, a spokesman for political advocacy group GetUp, an organiser of the pro-tax rally, said supporters for the carbon price plan had won the battle.

"We were overwhelmed with the amount of people that came out - the entirety of Treasury Place was packed," he said.