Several hundred protesters on Wednesday reached the 12-kilometer (seven-mile) fence surrounding the G-8 summit where U.S. President George W. Bush and German Chancellor Angela Merkel were to meet and police used water cannon on scattered stone-throwing demonstrators.
Other protesters blocked roads leading from the airport to the summit site of Heiligendamm on the Baltic Sea coast in northern Germany, as leaders began arriving on the first day of the three-day summit.
Another group swarmed over a small-gauge railway used to transport journalists to Heiligendamm from the summit center in nearby Kuehlungsborn, running in various directions until a detachment in riot gear corralled them in one area.
Police spokesman Manfred Luetjann said that protesters had managed to block two routes leading from the airport in Rostock and also breached security to reach the imposing fence surrounding the resort.
"We wanted to prevent this from happening but now they are there and we are handling it," he told The Associated Press by telephone.
He said that several thousand protesters were along parts of the fence, some throwing stones at police, who responded with water cannon. It was not immediately clear if there were any injuries or arrests.
Another police spokesman, Frank Scheulen, said most of the demonstrators who had reached the fence were peaceful, "but of course we have to assume that there could be potentially violent protesters among them."
"We will take all necessary measures" to ensure security, he said.
Luetjann said that protesters had blocked the A19 and B105 roadways from Laage airport, where Air Force One landed the day before, and where leaders including Russia's Vladimir Putin and Britain's Tony Blair were expected later in the day.
Luetjann said that journalists would be taken to the summit site by boat temporarily after the rail track was blocked.
Some of the demonstrators got to the barbed wire-topped fence, which runs through open countryside outside Heiligendamm. "The fence was reach by several hundred persons," said police spokesman Lueder Behrens.