Tens of thousands of people marched through the city as part of a global "Day of Action" of climate rallies from Australia to the United States, but violence flared at one stage when demonstrators smashed windows and set fire to cars.

Riot police detained more than 900 people around the Danish capital after black-clad activists threw bottles and smashed windows. A police spokeswoman said the number had climbed to 968 shortly after 10 p.m. (2100 GMT).

Police said four cars were set on fire during the evening. One policeman was hurt by a stone and a Swedish man injured by a firework.

"You don't have to use that kind of violence to be heard," said Connie Hedegaard, the Danish minister presiding at the UN talks. She condemned rioters after welcoming the main march at a candlelit vigil outside the conference centre.

One activist group accused the police of abuse after they detained around 400 black-clad demonstrators at the back of the march and forced them to sit on a road for hours in near-freezing temperatures, hands bound behind their backs.

The main demonstration was led by dancers, drummers and banners proclaiming: "There is no planet B" and "Change the politics, not the climate". Some activists were dressed as penguins with signs reading: "Save the Humans!"

They marched to the conference centre on the outskirts of the city, where negotiators from 192 nations are meeting from Dec. 7-18 hoping to agree a new U.N. climate pact.

Organisers said up to 100,000 people took part in the march, hoping their rally and others round the world would put pressure on a concluding summit of 110 world leaders on Thursday and Friday.

The procession wound its way from the Folketing, the parliament, to the conference venue, the massive Bella Centre outside the city centre.

On arrival at the site, the protesters presented a list of demands to Connie Hedegaard, a Danish cabinet minister serving as president of the conference, that runs until Dec 18.

Smaller solidarity demonstrations also took place in Greece, Spain, Germany and more than 100 other countries.

Former Danish supermodel Helena Christensen appealed to US President Barack Obama to lead a far-reaching pact when he comes to the UN climate summit at the end of next week.

"The United States must recognize the huge influence they have over what can happen in climate protection," she told the rally Saturday in the Danish capital.

Environment ministers, heads of government and other representatives of 191 states are due in Copenhagen next week to sign a Protocol on limiting greenhouse gases.

"How long do the heads of state want to sit back and watch how people are dying where we are because of climate change," said singer Angelique Kidjou from the West African nation of Benin.

Despite the arrests, police said the rally was generally peaceful.

The protesters demanded a far-reaching climate accord and large-scale transfers from rich countries to help poor ones adapt to climate change.

More than 5,000 officers were on duty to guard against violent outbursts. The Danish parliament previously passed special measures for punishing crimes committed during the climate summit.

The Copenhagen conference began circulating official drafts of an accord Friday, looking for a reduction in greenhouse gases for industrialised and developing nations.

In Brussels, EU officials said the drafts were "not adequate" and will have to be toughened.