Tens of thousands of demonstrators poured into the streets Sunday to protest the Group of Eight (search) summit across Lake Geneva (search) in the French town of Evian, some battling with police and looting shops and gas stations.

Anti-riot agents struck back with tear gas, water cannons and rubber pellets, as clashes continued into the evening.

German police brought in to bolster Swiss forces fought pitched battles with several hundred militants late Sunday in the center of Geneva. Swiss police simultaneously closed in on a youth cultural center that acted as a base for the protesters. The elegant streets of the lakeside city were turned into a sea of glass and acrid smoke filled the air.

A British man was hospitalized with multiple bone fractures when a police officer cut a rope that held him suspended from a highway overpass and he fell into a river, authorities said. Police were investigating, but said the officer who cut the rope did not know the man was there.

Police reported 10 other injuries among protesters, none life-threatening. One police officer was also hurt. Authorities searching demonstrator camps for violent youths in black masks arrested at least six people in Lausanne and detained some 400 for identification checks. A further 30 people were detained in Geneva.

Protesters started early Sunday, timing their actions to coincide with the arrival of most of the G-8 leaders from the world's top seven industrialized countries and Russia. Most of the leaders landed at Geneva airport and traveled to Evian (search) by helicopter.

The demonstrators -- who numbered nearly 50,000 according to Swiss police officials and 120,000 according to protest organizers -- blocked traffic for hours on bridges and highways in the French and Swiss regions around Geneva.

But they failed in their goal to disrupt the arrival of G-8 leaders and delegations or penetrate the security cordon around the lakeside summit site of Evian.

The centerpiece was a double march, one beginning in the French town of Annemasse and the other in Geneva. The two marches joined on the Swiss side of the border, then headed together into France.

Tension flared when the demonstrators tried to return to Geneva and were confronted by rows of riot police intent on preventing a repeat of a rampage Saturday night, when youths marauded through the city center.

Sunday's clashes in Geneva lasted at least seven hours and were some of the worst the city had ever seen. At least one pharmacy was ransacked and bullet proof windows of banks were smashed as police and militants played a cat and mouse game.

Police drove the demonstrators from the main commercial district into an area which houses an alternative cultural center. They then charged the building and turned on water cannons in a display of force.

German police -- part of a contingent of 1,000 summoned to help overstretched Geneva forces -- chased rock throwing militants through narrow streets.

In Lausanne, militants erected burning barricades at dawn on a highway leading to Evian, and battled riot police who fired tear gas and water cannons. Some protesters also looted a gas station and a supermarket in Lausanne, and youths occupied the city's many bridges in Geneva.

The demonstrators waved banners criticizing the G-8, the World Trade Organization and other international bodies.

Some wore oversized masks lampooning G-8 leaders like President Bush and British Prime Minister Tony Blair.

The protesters support a wide array of concerns, from anti-globalization and environmentalism to forgiveness of Third World debt and fears over genetically modified foods. They accuse the G-8 of profiting on the misery of poorer nations.

Police in Lausanne said the British man was injured when authorities came to an overpass that demonstrators were blocking. Protesters had strung a rope across the road and hung an anti-G-8 banner. After the protesters dispersed, a policeman cut the rope, concerned that a car might hit it.

The 39-year-old Briton on the rope fell about 60 feet into a shallow stream. Police grabbed the other half of the rope, preventing a woman holding on to the opposite end from falling as well. Hospital officials said the man's life was not in danger.