UPDATE (at bottom): Biden appeals directly to G20 protesters
Tens of thousands of trade unionists, environmental campaigners and anti-globalisation activists took to the streets of London on Saturday to start five days of protests before the G20 summit.
Organisers of the Put People First march for "jobs, justice and climate" have rejected as "smears" claims in police briefings that the demonstration could be hijacked by anarchists bent on violence.
An alliance of more than 150 unions and environment, charity, faith and development groups will march through the capital from Victoria Embankment to Hyde Park to demand action to save jobs, create a low-carbon economy and impose stricter controls on the finance sector.
The general secretary of the Trade Union Congress, Brendan Barber, said: "Never before has such a wide coalition come together with such a clear message for world leaders.
"The old ideas of unregulated free markets do not work, and have brought the world's economy to near-collapse, failed to fight poverty and have done far too little to move to a low-carbon economy."
Britain's Climate Change minister Ed Miliband met campaigners before the march got under way and said the "vast majority" were planning to protest peacefully.
"I think the kind of campaigning that people are engaged in today -- certainly what the organisers intend, what the vast majority of the people who are going on this march will do -- is the kind of peaceful protest that is very much part of our society," he said.
Demonstrators travelled to London from all over the country. Organisers said they were expecting hundreds of thousands of people to join the march.
Later in the day, campaigners were set to target companies and buildings which fail to switch off their lights, even saying they will try to enter 'offending' tower blocks and offices.
That action is part of the global Earth Hour initiative which seeks to urge people to turn off the lights for an hour.
World leaders, including US President Barack Obama on his first visit to Europe since he took office, will gather in London on Thursday for the Group of 20 summit.
British Prime Minister Gordon Brown hopes the meeting will help set the world on the road to recovery from the deepest recession since the 1930s.
More mass protests are planned in London in the days leading up to the summit.
The police are most concerned about the potential for violence on Wednesday, dubbed "Financial Fools Day" by demonstrators, when an anti-war march will be held and climate change campaigners will set up a camp in the City of London financial district.
A British university professor has been suspended from his job after warning that bankers would be "hanging from lampposts" during the demonstrations, and finance workers have been warned to dress down to avoid attracting attention.
UPDATE: Biden appeals directly to G20 protesters
US Vice President Joe Biden on Saturday called for tens of thousands of protesters already on the streets of Europe ahead of a G20 summit next week to give governments a chance to tackle the economic crisis.
"I would hope that the protesters give us a chance, listen to what we have to say and hopefully we can make it clear to them that we're going to walk away from this G20 meeting with some concrete proposals," Biden said at a news conference after a meeting of center-left politicians in Chile.
Tens of thousands frustrated by the deepest global recession since the 1930s took to the streets of London Saturday, as well as thousands more in Paris, Berlin and Frankfurt, ahead of Thursday's summit of the Group of 20 industrialized and developing economies.
"The action that is happening in London today I understand, and we will respond to it at the G20," said British Prime Minister Gordon Brown, who will host the London meeting.
Biden added: "I would say to the protesters that unless we talk, unless we attempt to deal with this changed circumstance we find ourselves in, there is no solution. Things will only get worse."
Protesters in London plan a series of mass demos ahead of the G20 and have rejected police claims that they could be hijacked by anarchists bent on violence.
A university professor has been suspended from his job after warning that bankers would be "hanging from lampposts" during the protests, and finance workers have been advised to dress down to avoid attracting attention.
This video is from Al Jazeera English, published to YouTube March 28, 2009.