Police used water cannon to disperse groups of protesters trying to disrupt a Group of Eight (G8) meeting of world leaders on Wednesday, police said.
Police spokesman Luedger Behrens said officers "used water cannons twice after demonstrators bombarded police with stones."
He said roughly 10,000 demonstrators were violating a ban on demonstrations in the area around the summit and risked being detained.
The demonstrators northeast of the town of Bad Doberan were trying to make their way to a high security fence and block access to the hotel in Heiligendamm where G8 leaders were due to meet.
Some demonstrators used trees and rocks to block the main access road to the resort, a shady, tree-line avenue linking the towns of Bad Doberan and Heiligendamm on the Baltic Sea coast.
Police said they were shuttling in reinforcements to Bad Doberan by helicopter.