Conservative Prime Minister John Howard and premiers of the three worst-hit states were presented with the bleak assessment at the meeting in Canberra by an expert on the country's most significant river system, participants said.

The drought has already been described variously as the worst in living memory, the worst in a century and the worst since white settlement more than two centuries ago.

Howard said he could not verify the latest claim.

"You say worst drought in a thousand years. I don't think anybody really knows that," he said, adding that he was not a scientist. "It's a very bad drought," he said.

The comparison was made by the general manager of River Murray Water, David Dreverman.

Howard had called the summit as statistics showed that the country's most important river system, within the Murray-Darling Basin, could run out of water in six months, after six years of drought.

About 30 rivers and hundreds of tributaries run across the basin, which feeds about 70 per cent of Australia's irrigated farmlands.

South Australian Premier Mike Rann said the assessment by Dreverman, who also sits on the Murray-Darling Basin Commission, was worrying.

"We were told at the meeting by the Murray-Darling commissioner that we now face, not a one-in-100-year drought, but a one-in-1,000-year drought," Rann told reporters. "So we are into uncharted territory."

The summit agreed to draw up contingency plans to secure water supplies, with a working group of state and federal public servants to report back by December 15.

The "big dry", as the drought is called here, is likely to cut agricultural output by 20 percent and GDP by around 0.7 percent, government officials say.

With an electorate increasingly ready to blame the drought on global warming, Howard has abandoned his previously sceptical response to the idea that pollution is driving climate change.

An ACNielsen poll published in Tuesday's Sydney Morning Herald showed that 91 percent of Australians believe global warming is a problem and 62 percent of voters are unhappy with the government's response.

Howard's conversion to environmental activism has been noticeably sudden, with opposition leaders and political commentators noting that climate change is shaping up as a major issue in elections due next year.

Just two months ago Howard spurned a meeting with former US vice-president Al Gore, who was in Australia to promote his global warming documentary "An Inconvenient Truth", saying he did not take policy advice from films.

Last month, as evidence of the consequences of global warming mounted, he announced that 500 million dollars (385 million US) would be spent on a series of clean energy initiatives.

Howard's apparent conversion coincides with that of a fellow conservative Australian, media mogul Rupert Murdoch, who said Monday in Japan that he now believed global action was needed.

All rights reserved. � 2005 Agence France-Presse. Sections of the information displayed on this page (dispatches, photographs, logos) are protected by intellectual property rights owned by Agence France-Presse. As a consequence, you may not copy, reproduce, modify, transmit, publish, display or in any way commercially exploit any of the content of this section without the prior written consent of Agence France-Presse.