Thousands of people rallied in Hamburg yesterday to protest at next week's G-20 summit, where U.S. President Donald Trump is make his maiden appearance at the forum of major economies. The gathering outside city hall took place in parallel with protests by canoeists on the nearby river Alster, while in the port of Hamburg, Greenpeace staged a climate demonstration near a ship laden with coal. The Group of 20 G20 comprises leaders of the world's major industrialized and emerging economies. The G-20 summit will take place on July 7 and 8 and bring together leaders including Turkish President Recep Tayyip Erdoğan, U.S. President Donald Trump and Russian President Vladimir Putin.Hamburg, where summit host Chancellor Angela Merkel was born, is a bustling city that is also an anti-establishment bastion. Around 30 protests have been scheduled ahead of the summit, and the organizers are hoping for a total turnout of more than 100,000 people. Hamburg is a citadel of leftwing radicals, and the authorities say they are bracing for possible clashes and property damage.Interior Minister Thomas de Maiziere, in the Sunday edition of the daily Bild, warned that any violence "should be nipped in the bud". "Freedom of assembly is only valid for peaceful demonstrations," he said. Around 15,000 police will be deployed to protect the summit, in addition to 3,800 officers monitoring airport and train security.