Officers in helmets and body armor at one point briefly retreated before a hail of stones, while other officers chased down fleeing protesters at the rally in Rostock in northern Germany.

Police marched in a line 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."

Cordula Feitchinger, a police spokeswoman, said one officer was slightly injured. She had no immediate total for arrests.

"There are massive assaults on police officers at the city's harbor right now," police spokeswoman Cordula Feichtinger said. "The situation is currently very chaotic and we have to get it under control before I can tell you how many people have been arrested."

Feichtinger said one police officer was slightly injured but remained on duty.

The officially permitted march took place before the three-day summit beginning Wednesday 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.

Earlier, a group of protesters attacked the hotel where an American delegation was supposed to stay during the G-8 summit this week, and some demonstrators also battered police cars with rocks, bottles and paint bombs, authorities said.