"We will move the world ahead. We will not wait for (US President) George W. Bush," Elizabeth May of the Sierra Club environmental group told the crowd, estimated at about 6,000 people.

"Together we can save the climate. Together we will stop fossil fuels from destroying our future," she said outside the Montreal conference center, where 189 nations are meeting from Nov. 28-Dec. 9 to find ways to halt climate change.

Delegates are discussing the shape of the next phase of the UN's Kyoto Protocol climate pact, but discussions are being hampered between those who back emission reduction targets and outsiders, such as Washington, which are opposed to caps.

Organizers said similar marches were held in 30 cities from Sydney to London to urge governments to lower emissions of heat-trapping gases from burning fossil fuels in factories, power plants and cars.

In Montreal, one man walked on stilts disguised as the grim reaper, while others wore panda or polar bear costumes. "The ice is melting, we're suffering the most, we can't get food," said Gordon Shepherd, a Scottish activist dressed as a polar bear.

Canadian Foreign Minister Pierre Pettigrew and Environment Minister Stephane Dion took part in the march. Some protesters booed the ministers, accusing them of doing too little, but the harshest criticisms were for Bush.

"Wake up USA!," one banner read. "George, you're not alone on this planet!" another said.

In 2001, Bush pulled out of the UN's Kyoto Protocol, which binds about 40 industrial nations to cut emissions of greenhouse gases by 5 percent below 1990 levels by 2008-2012.

STIFLE GROWTH

Bush says Kyoto would stifle economic growth and wrongly excludes poor countries from a first round of targets to 2012. Washington doubts that greenhouse gases will mean catastrophic floods, droughts and rising sea levels.

The Montreal talks are seeking ways to enlist both the United States and poor nations such as China and India in discussing ways to combat climate change beyond 2012.

Washington has said it is not interested in joining new talks but Canadian negotiators say they have not given up hope.

"We want these talks to end with an agreement to start discussions about the future," a senior Canadian official said.

In London, thousands of protesters, some blowing whistles and carrying banners, accused British Prime Minister Tony Blair of wavering on pledges to make deep carbon reduction targets beyond 2012. "No Blair betrayal on climate" one banner read.

"We're seeing greenhouse gas emissions rise under this government. We're seeing this government now not talking about targets, talking about technology instead," said Caroline Lucas, a leading member of Britain's Green party.