Riot police were deployed as a precaution and officers videotaped the demonstration.Some protesters covered their heads and faces with black hoods, sunglasses and scarves, while others chanted protest slogans through megaphones, blowing whistles and waving flags.
A group of protesters attacked police cars with rocks, bottles and paint bombs, authorities said, adding that a hotel where a US delegation is supposed to stay during the G-8 summit was also attacked.
Windows smashed
Rocks and broken beer bottles lay on the ground in front of a bank building where protesters smashed half a dozen windows.
Most stores along the route had boarded up there windows before the protests - with the exception of sausage stands and other fast food restaurants.
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 existence of the G-8 itself.
"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," organisers said in leaflets handed out on the streets.
"We want to protest against this and show the alternatives."
High alert
A 12km security fence has been built around the resort where for the June 6-8 talks about climate change, aid and financial markets.
Eager to avert the violence that has accompanied past G8 summits, German leaders have issued pleas for peaceful demonstrations.
In 2001, a demonstrator was shot by police at a G8 meeting in Genoa. Since then, G8 summits have been surrounded by heavy security.
About 16,000 police officers are on duty in the week leading up to the meeting, Germany's biggest security operation since after World War II.
Roadblocks expected
Protesters are expected to block roads leading to the summit.
They may also disrupt the arrival of delegates with their plan to blockade the nearby military airport at Rostock-Laage early next week.
Trouble may also flare after authorities refused permission for a demonstration by the far-right National Democrats (NPD) to go ahead in nearby Schwerin.
Organisers of the main anti-G8 demonstrations expressed concern that protesters who had planned to take part in the Schwerin rally might descend on Rostock instead.
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