SYDNEY, Dec 12 (Reuters) - Thousands took to the streets of Australia's main cities on Saturday at the start of an international day of action to pressure the U.N. conference in Copenhagen for strong action on climate change, organisers said.

Australia's 'Walk Against Warming' was held in all the country's main cities, to urge politicians to take bold measures to curb greenhouse gas emissions and make a deal to replace the Kyoto protocol.

In Melbourne, where the largest protest was held, marchers closed the event by spelling out the words 'Safe Climate - Do It!' on the ground. Organisers said aerial photographs were taken and sent to delegates in Copenhagen.

Tricia Phelan, who organised that event, said the turnout was evidence to the Copenhagen conference that Australia was "absolutely behind" firm action on climate change.

Protesters in Sydney carried placards saying "I like clean energy and I vote", "No meat, no heat" and "No new coal mines", a reference to Australia's status as one of the world's leading exporters of coal.

Jamnes Danenberg, organiser in Adelaide, said the events had a clear message for the conference.

"The message in a nutshell is that Australians want action for a safe climate future,' Danenberg told Reuters. "We are all in this together and it is our world in their hands."

Police contacted by Reuters declined to give figures for the protests, confirming only that the Melbourne protest numbered in the thousands. However, organisers told Reuters police at the scene had told them the official police estimate was 40,000.

In Sydney, a Reuters photographer estimated the crowd as in the thousands.

The protests follow a failed attempt by the Labor government to set up an emissions trading scheme, after climate change sceptics in the conservative opposition blocked it in the upper house Senate.

Australia is one of the world's largest per capita emitters of greenhouse gases and relies heavily on coal for its electricity.

(Editing by Bill Tarrant)

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