COPENHAGEN — Waving a panoply of signs warning that the planet is in peril and that powerful nations should take note, tens of thousands of demonstrators from around the globe took to the streets here on Saturday for the largest protest planned in two weeks of talks on a global strategy to combat climate change.

Johan Spanner for The New York Times

Protesters converged in a Copenhagen square Saturday to urge conference delegates to reach a global climate agreement.

The police and organizers estimated that 60,000 to 100,000 participants joined a long march from Christiansborg Slotsplads, or Castle Square, southward to the Bella Center, the sprawling and heavily fortified convention center where delegates and observers from nearly 200 nations are gathered to seek a consensus.

The main demonstration — which brought together a broad coalition of hundreds of environmental groups, human rights campaigners, climate activists, anticapitalists and freelance protesters from dozens of countries — was mostly peaceful. But in other parts of the city, spontaneous demonstrations by bands of radical protesters resulted in at least 950 arrests, the police said.

A spokeswoman for the police department said there were scattered reports of localized riots in which protesters threw rocks and smashed windows. The police said that four parked cars had been set ablaze in the Christiana neighborhood and that at least one police officer had been struck in the jaw by a rock.

“We saved the demonstration from being disturbed totally,” said Per Larsen, chief coordinator for the Danish police. “There were some hard-core protesters that we have neutralized.”

The violence was a counterpoint to the otherwise peaceful march, in which a rolling sea of flags and banners undulated across the city. Most bore slogans related to global warming or urging world leaders to resolve the vast differences that still make an international accord seem elusive as talks here move into the second and final week.

“Bla, Bla, Bla,” read one popular sign. “Act Now!”

On a stage at the eastern edge of the square, a succession of speakers stoked a cheering crowd, their voices booming over loudspeakers. “My words cannot replace action,” said Helle Thorning-Schmidt, the leader of Denmark’s Social Democrats, the dominant opposition party here. “We are here to show leaders that what is made by man, can be changed by man.”

In the throng was 26-year-old Jemimah Maitei, dressed in traditional clothing from her native Kenya. She said she had traveled to Copenhagen to be part of a delegation representing indigenous peoples at the talks, which are overseen by the United Nations.

“I came here to give my views on how climate change is impacting my community,” Ms. Maitei said. She cited relentless droughts that had made growing crops, among other things, increasingly difficult for the Masai, her ethnic group.

The vast demonstration, which unfolded in crisp temperatures under cloudless skies, was not the exclusive province of climate campaigners. Groups of diverse social and political pedigree took advantage of the huge gathering to advance their agendas, too. One sign urged the overthrow of the Iranian government. Another, with the words “Earth in Need: Delete Meat,” was one of many promoting vegetarian diets.

People calling for a free Tibet were well represented, and a small contingent of climate skeptics and libertarians derided the United Nations talks.

“We want to be able to live our lives like we’ve always led them before — as free citizens in free democracies,” said David Pontoppidan, a graduate student in sociology at the University of Copenhagen, who addressed passers-by through a megaphone over the chatter of two helicopters hovering far above. “We want free debate; we want to be able to be taken seriously even though we don’t agree with the U.N.”

By midafternoon, as the throng made its way over the canal and southward toward the Bella Center, small bands of black-clad youths chanting anticapitalist slogans and carrying sticks and rocks could be seen infiltrating the otherwise peaceful crowd.

At around 3:30, dozens of Danish police officers penetrated the parade near its tail and surrounded a group of the more radical protesters. At the end of the march, a stage was set up for more speeches. One speaker railed against nuclear power, and another against genetically modified food. A speaker from India demanded that rich nations provide technology to develop flood- and drought-resistant crops.

Given that the lion’s share of greenhouse gases have been emitted by industrialized nations, developing countries have argued that they have a duty to help poor lands deal with the consequences of global warming, including drought, floods and tropical storms.

While several demonstrators made for the Metro trains, others decided to avoid the crush of the crowds and walk back to the city the way they came. Among them were Lars Leffland and Lise Blaase, a couple from Copenhagen.

“The demonstration when it started was very beautiful with all the colors and the music,” Mr. Leffland said. But Ms. Blaase suggested that what had begun with exuberance seemed, in the end, to simply fizzle.

“It was somewhat of an anticlimax,” she said as she walked north away from the Bella Center. “It seemed as if no one was in charge, and there was no closure.”