Left-wing protesters have rallied in the German alpine town of Garmisch-Partenkirchen ahead of the meeting of world leaders. Police says they have already come under attack.
Police are warning that "extremists" have arrived at the G7 summit in southern Germany.
A force of around 20,000 police officers kept a close eye on several thousand protesters on Saturday, gathering in the German resort town of Garmisch-Partenkirchen. There had been fears of widespread violence in the lead-up to the event, with organizers expecting around 10,000 people to show up.
Spokesman Hans-Peter Kammerer said there were large numbers of far-left radicals from Germany, Austria, Italy and Britain among them.
Ahead of the summit, which begins Sunday, police officials said they came under attack with bottles and fire extinguishers, and that officers had used pepper spray on protesters.
There were scattered reports of injuries and scuffles breaking out. Protesters also accused police of using batons, and posted tweets telling attendees to stay calm and to not let themselves be intimidated.
Numbers varied between 2,000 and 5,000, with more demonstrators expected to arrive before leaders of the G7 nations - Germany, the United States, Britain, Canada, Italy, France and Japan, along with the European Union - meet on Sunday.
Officials will be hosted at the Elmau luxury alpine hotel, around 10 kilometers (6 miles) away from the town.
The G7 meeting has proved to be a magnet for left-wing protest movements, attracting anti-capitalists, environmental activists, pro-refugee groups and many more.
"I'm protesting because the big financial corporations have too much influence over politics," said 50-year-old Thomas Schmidbauer.
"We could organize our economies much better for the people."
Some demonstrators chanted slogans damning police violence, some brandished signs with anti-war statements, while others rallied against a proposed transatlantic trade deal.
Despite the reports of violence, most described the mood as otherwise festive, with members of protest group "Stop G7 Elmau" talking of participants in costume, playing music and dancing at the "cheerful" protest. A tent city set up by demonstrators even attracted curious locals.
On Thursday there were rallies held in the Bavarian capital of Munich, focusing on the environment and globalization. A court ruling earlier in the week to allow 50 protesters inside the security zone so that world leaders could hear their message did little to satisfy protesters' spokesman Simon Ernst.
"We think it shows an arrogant attitude towards freedom of assembly," he said.
Sticking to the agenda
This weekend's meeting will be the second without Russia, which was expelled from the G8 over its annexation of the Crimean peninsula last year. One of the main topics of discussion is expected to be the crisis in Ukraine, with the recent uptick in fighting along the border worrying the international community.
Some demonstrators worried Russia's exclusion would exacerbate tensions.
"We're seeing the beginning of a Cold War now with both sides rattling their sabres," said Rainer Lipfert, wearing a t-shirt with the words "Putin sympathizer."
Leaders are also expected to discuss topics such as climate change, women's rights and alleviating world poverty, as well Greece's debt crisis. On Monday they will meet with officials from Iraq, Tunisia and Nigeria, over the fight against terror groups Islamic State and Boko Haram.
Leaders will begin arriving on Saturday in preparation for the conference, although US President Barack Obama is only expected to fly in early on Sunday.
an/sgb (AFP, dpa, Reuters, AP, EPD, KNA)