LONDON — Thousands of people marched through European cities Saturday to demand jobs, economic justice and environmental accountability, kicking off six days of protest and action planned in the run-up to the G-20 summit next week in London.

In London, more than 150 groups threw their backing behind the "Put People First" march. Police said around 35,000 attended the demonstration, snaking their way across the city toward Speaker's Corner in Hyde Park. Protest organizers said they wanted leaders from the world's top 20 economies to adopt a more transparent and democratic economic recovery plan.

Brendan Barber, who heads an umbrella group for Britain's unions, told assembled protesters in London's Hyde Park that the G-20 needed to "take actions to lay the foundation for a better world."

"If we can generate fabulous wealth, as we can, then surely we can learn how to distribute that wealth more fairly. If we can unleash a technological revolution then surely we can ensure that everyone on this planet gets the food, the shelter and the health care that they need," he said.

Not all demonstrators focused on the economic main message. Some chanted "Free, free, Palestine." One man dressed in a banana suit waved a sign reading: "Bananas for Justice."

Big protests were also held in Germany. Around 15,000 people gathered in Berlin, and a demonstration also was held in Frankfurt, Germany's banking capital, under the slogan: "We won't pay for your crisis."

Demonstrators in Berlin sported headbands reading "pay for it yourselves" and some carried a black coffin topped with red roses symbolizing what they said was the death of capitalism.

Some protesters in Berlin skirmished with police toward the end of the demonstration, and the windows of some police cars were broken.

In Vienna, around 6,500 people gathered in the city center, with paper piggy banks, balloons or signs that read "We won't pay for your crisis" and "Capitalism can't be reformed." Others blew whistles, chanted or danced to music blasting from trucks or a stage in front of parliament.

In Paris, a small but focused group of around 400 protesters dumped a pile of sand outside the city's stock market to mock supposed island tax havens. Protesters sat atop the sand pile in beach chairs — tossing around colored bills with "5,000 euros, tax free" written on them.

Trade unions and left-wing groups in Geneva mobilized some 250 people who marched through town with banners reading "Capitalism is a mistake" and chants of "Revolution."

More protests are planned in London on Wednesday and Thursday, while left-leaning teach-ins, lectures, and other demonstrations are scheduled throughout the week. Protesters said the crisis could energize those hoping to challenge the economic and political status quo.

"The whole economic meltdown ... There's a really good opportunity for governments to get together and invest in a sustainable future," said unemployed Steve Burson, 49.

Security was tight around a small group of people waving anarchist flags Saturday. They and others have promised violence before the G-20 meeting Thursday, and the British capital is bracing for a massive police operation as delegates fly in to London.

"We've got a long week ahead," said Christian Evans, 40, an anarchist supporter flanked by black and red flags in London. "The streets are our streets."