Merkel chose Hamburg, the port city where she was born, to send a signal about Germany's openness to the world, including its tolerance of peaceful protests.
Heavily armed police commandos moved in after activists had spent much of the day attempting to wrest control of the streets from more than 15,000 police, setting fires, looting and building barricades.
Police have arrested 114 people, according to AP, including one man who is being held on suspicion of attempted murder for using a laser to temporarily blind the pilot of a police helicopter. In 2009, before the London summit, the London police drew on a sit-down protest of about 4,000 members.
Hamburg police said at least 45 people had been arrested during protests on Thursday and Friday.
Donald Trump and Vladimir Putin met for the first time on Friday at the G20 Summit in Hamburg, Germany, in a highly anticipated encounter before their official bilateral meeting later in the day. But they continued to talk for another hour after that, Tillerson said.
Around 1,000 police officers have arrived in Hamburg to support security forces.
Protesters repeatedly tried pushing into the no-go zone - among them a group of 22 swimmers from Greenpeace who tried accessing the area from the Elbe River but did not succeed, police said.
At first police stayed back while the protesters took a hit-and-run approach, groups of them running up the road, throwing rocks and bottles, and quickly retreating.
Turkey's sweeping arrests of alleged state enemies after last year's coup attempt and a dispute centred on a North Atlantic Treaty Organisation base "are developments which I, of course, raised that show deep differences", Merkel said. "But here the discussions are very hard, I don't want to talk around that". He added that more than 20,000 police officers were on duty. With the organizers anticipating trouble, the maps bore a warning: "Take enough water and a first-aid kit with you - and don't wear contact lenses", in case the police used tear gas or pepper spray.
"There's a need for change to stop the destroying of the planet and of the resources", he said in an interview Friday.
The US joined the states of Nicaragua and Syria in rejecting the Paris Climate Agreement when Mr Trump announced his decision in June. According to the report, a spokesperson for the USA delegation told German media that they were unable to get clearance for Melania to leave the hotel in which she is staying.
French President Emmanuel Macron said he would be hosting a summit in Paris in December with a view to taking new actions on climate. "It's unfortunate", Grisham said.
Spouses of world leaders were invited to a boat ride, lunch and a tour of a climate control center, according to The Associated Press. CNN saw people who were injured but police tweeted there were no totals available for how many people were hurt.style="text-align: center;"