An estimated 60,000 people have attended rallies across Australia in one of the largest ever displays of support for action on climate change.

Labor and Greens politicians, alongside volunteer firefighters and environmental activists, took turns at the Climate Action Day to lambast the Coalition government, which will table bills in parliament on Monday to dismantle carbon pricing.

Around 25,000 people gathered on Sunday in the Melbourne sunshine, with Labor's environment spokesman, Mark Butler, reaffirming to the crowd that the opposition would not back down in its support for carbon pricing.

"In Australia, unlike in most other countries, there's an atmosphere of denialism and scepticism," he said. "So many in our media and so many of our politicians, who should know better, deny that the science is settled.

"This isn't the time to move backwards. You'll hear a lot this week from Tony Abbott about his mandate. He'll tell all of you to get out of the way as he tries to slam Australia into reverse. But we won't be taking a backwards step, not this week, not this year, or next year or ever."

The Greens' deputy leader, Adam Bandt, told the gathering that Australia needed a "Churchill rather than a Chamberlain" on climate, while Peter Marshall of the United Firefighters Union said an increase in the number of severe bushfires meant there were "no climate sceptics on the end of a fire hose" among volunteer fire crews.

Tim Flannery, head of the Climate Commission, which was axed by the Coalition after it took power, urged the crowd to use "every effort within the law to slow the uptake of fossil fuels".

"If we let we let the world get warmer it'll have an impact on fire weather and the ocean is going to expand," he said. "These are pretty simple propositions, they aren't propositions for argument by anyone. They need to be accepted as the facts and we need to move forward with the risk in our mind."

About 10,000 people attended a rain-drenched rally in Sydney addressed by the Labor deputy leader, Tanya Plibersek. About 5,000 turned up in Brisbane and across Australia more than 130 events were held in capital cities and regional towns, organisers said.

The rallies, by early estimates from organisers, will have attracted more people than the Walk Against Warming events in 2006, in which 40,000 people urged then-prime minister John Howard to do more on the issue of climate change.

Activist group GetUp, along with environmental lobby groups Australian Conservation Foundation and Greenpeace, organised the events.

Sam Mclean, GetUp's national director, denied that the Coalition had the broad support of the public for its aim of scrapping carbon pricing in favour of its Direct Action policy, in which businesses will be offered incentives to reduce emissions.

"In any analysis of the election Tony Abbott has no mandate to go backwards on climate change," Mclean said. "Our own polling has shown that 69% of people want stronger action on climate change. We need to know what Tony Abbott will do, because the policy he has outlined so far is a joke."