Thousands of anti-capitalists poured into the French Riviera city of Nice on Tuesday for a march against corporate greed ahead of the G20 summit in nearby Cannes, echoing protests worldwide.

Shouting "People first, not finance!", protesters from around Europe and beyond marched noisily along their assigned route in the city's outskirts on a sunny and peaceful national holiday in the Mediterranean city.

They have been arriving since Monday at the "Old Abattoir" cultural centre where a "People's Summit" is to be held in parallel to the summit of Group of 20 leaders around 30 kilometres (20 miles) down the Mediterranean coast on Thursday and Friday.

Police estimates put the number of demonstrators in Tuesday's march at 5,400, while organisers, who say 10,000-12,000 took part, hailed the event a great success.

"The turnout is above that which we were expecting," said spokesman Franck Gaye.

"We have received a good welcome, people are waving at us from their windows ... I hope that the governments are going to listen to the people," he added.

Around 100 Oxfam activists came from Spain, Belgium, Mexico, Britain and France, many wearing Robin Hood hats and carrying jute bags representing the stock exchange, demanding a tax on financial transaction.

"I am Robin Hood, I demand (French President) Nicolas Sarkozy set up a tax on financial transactions. We take from the rich to give to the poor, we want a better distribution of wealth," said Benjamin Lemesle, 23.

Two backpacker protesters, from Belgium and France, arrived on a train from Paris and told AFP they "came to Nice to ask for just a little more humanity (and for) the financial system to be put at the people's service."

Police in Nice said they had arrested three Spanish men on the city's renowned Promenade des Anglais seafront in possession of "bolts, mountaineering axes, balaclavas and gas masks" ahead of the march.

Interior ministry spokesman Pierre-Henry Brandet said the men had T-shirts and badges with "Black Cross" written on them, which he said suggested they may be part of the militant Black Bloc protest movement.

Anyone thought to be associated with Black Bloc protests faces arrest if police find them anywhere in the region.

Officers also arrested two Belgians armed with steel weapons near the train station ahead of the march, a police source said. Not thought to be part of a specific movement, the two were released after the demonstration.

Groups including environmental advocates Greenpeace, Attac, the Human Rights League and anti-racism organisations organised the march, which culminated at the "Old Abattoir" in the early evening.

Some 2,500 extra police were drafted in to deal with the protest and about 15 vehicles belonging to the CRS riot police were parked in front of Nice's train station, with groups of riot police patrolling the station, stopping passengers to search them and check their identities.

Paris obtained authorisation from Brussels to reintroduce customs and immigration checks on the Italian border to prevent troublemakers gaining entry after around 100 people were injured in violent protests in Rome on October 15.

One of the protest's organisers, Franck Gaye, said ahead of the march that there would be no confrontation in Nice as anarchist movements "have called on supporters to go everywhere in France because there won't be security forces elsewhere."

On Thursday, some protesters will head to the principality of Monaco to "celebrate" the end of tax havens that was announced at the 2009 G20 summit in London.

Anti-capitalism protests have sprung up in more than 80 countries in recent months, including a protest camp in the heart of London's City financial district, the Occupy Wall Street movement in the United States and the Indignants protesters in Spain.

The protests are against what demonstrators consider an irresponsible financial system and for economic equality.