The name pretty much says it all: "Welcome to Hell!" One of the largest anti-G-20 protests is scheduled to begin at 4 p.m. local time in Hamburg today. Police say they plan to take decisive action against far-left activists with the "Black Bloc" autonomist movement if the protests turn violent. Following a peaceful protest attended by 11,000 people on Wednesday night, police are bracing for Thursday's "Welcome to Hell" demo, Hamburg Police Chief Ralf Martin Meyer told public broadcaster ZDF on Thursday morning.

"The largest Black Bloc of all time has been announced by the Rote Flora (a left-wing political center in Hamburg that has been the center of protests in the past), by the autonomists. And afterwards, things could get dicey afterwards. 'Welcome to Hell" doesn't sound like sit-ins or verbal protests, but like something more -- that's why we're skeptical whether tonight will remain peaceful," Meyer said. "The numbers are such that we are positioning ourselves well with strong forces -- and that will certainly become necessary in order to take decisive action if crimes are committed." Police say their primary concern is the security of summit participants, the people and peaceful protesters.