Thousands of anti-globalisation activists, left-wing groups, students and anarchists have gathered in northern Germany to demonstrate outside the G8 summit.
Some 16,000 police have been deployed near the seaside resort of Heiligendamm, where the leaders of the eight top industrialised nations are meeting.
The protesters have attempted to cut off all ground access to the summit.
The broad range of groups rallying at the summit say they have one overarching common interest - social justice.
The main protest planned for Thursday was cancelled after being banned, but some clashes continued.
Police also used water cannon to disperse stubborn protesters.
A number of protesters and policemen have been injured in ongoing clashes over the past two days.
Two Greenpeace boats failed to break through a Baltic Sea cordon as they tried to deliver a message to G8 leaders.