Masked demonstrators showered police with rocks and beer bottles, then were driven back with water cannons and tear gas during a protest march Saturday against the upcoming Group of Eight summit in Germany. The clashes left smoke from burning cars and the sting of tear gas drifting through the harbor front area in the north German port of Rostock. Some 146 police were hurt, 25 of them seriously. There was no immediate information on whether any protesters were injured. The officially permitted march preceded a three-day summit beginning Wednesday in the seaside resort of Heiligendamm, where German Chancellor Angela Merkel hosts the leaders of the other G-8 nations - Britain, France, Japan, Italy, Russia, Canada and the United States. The leaders are expected to discuss measures against global warming, the fight against AIDS and poverty in Africa and the world economy. As in previous years, the summit has drawn protesters of various stripes, opposed to globalization, capitalism or the G-8 itself. Most marchers were peaceful, but others pried up paving stones and broke them into throwing-sized pieces before charging police. Officers in helmets and full body armor fell back, then charged the demonstrators. Five large green police trucks with twin water cannons mounted on top blasted groups of rioters. A police car was destroyed and several parked cars burned, spreading black smoke over the area. Radicals "are smashing everything in their way to pieces," said police spokesman Karsten Wolff. There were no immediate numbers for arrests. Police spokesman Frank Scheulen estimated the number of violence-minded demonstrators at about 2,000. Police put the size of the demonstration at 25,000, while organizers said it was 80,000. Officials said 17 people were arrested; the police in some cases were content to subdue unruly demonstrators but then let them go. Werner Raetz, an anti-globalization activist with Attac, one of the organizing groups, distanced himself from violent protesters. "There is no justification for these attacks," he said. As for the further demonstrations that are planned for next week, Raetz said both sides should try to get the "emotional situation" under control. Police have built a 12-kilometer fence around the summit site at Heiligendamm and banned protests in the immediate area. There are several camps in the area for protesters and marches are planned. Demonstrator Peter Mueller had tears streaming from bloodshot eyes after the tear gas was released. "As long as the police were in the background it was OK, but as soon as one took a step closer, it went out of control," he said. He shrugged. "What can you do? So ends the peaceful protest." At one point, a long line of police marched through a harborside street to scatter demonstrators, and were pelted with stones from behind. One of the organizers pleaded for calm from a loudspeaker. "The police are heading back so we can hold our protest in peace, that is what we want," he said. The march began without violence, and most of the demonstrators remained peaceful, gathering to listen to speeches from a stage in a large square near the waterfront. But some taunted members of the 13,000-strong police detachment from around Germany, and several hundred wore bandanas across their faces with sweat shirt hoods pulled down low to obscure their identities. The protesters from around Europe and the world gathered at two locations early in the day for rallies, then marched in two groups along 4-kilometer (3-mile) routes to converge on the harbor for the main demonstration. Police lined the path through the city, and helicopters flew overhead. Most shops and cafes were shuttered. The protest was organized by several dozen groups under the motto "another world is possible." "The world shaped by the dominance of the G-8 is a world of war, hunger, social divisions, environmental destruction and barriers against migrants and refugees," organizers said in leaflets handed out on the streets. "We want to protest against this and show the alternatives." Dozens of different groups, including communists, anarchists and environmentalists, were taking part and messages were mixed: Some urged action from the G-8 countries in the fight against HIV/AIDS, African poverty and climate change, while others questioned the legitimacy of the G-8 meeting itself. Protester Kay Stenzel got up at 3 a.m. to drive in from the eastern city of Bautzen with four friends to voice his discontent with the G-8 leaders. "They want to impose their wills upon the poor nations," he said at the meeting point outside Rostock's main train station. He waved a red flag onto which he had painted a black cat, an animal he chose because it was "unruly." On their Web site, organizers emphasized that they wanted a peaceful protest. "There is no reason to be afraid to come to the big demonstration in Rostock," they said. "We do not expect major problems with the police."