HAMBURG, Germany (AP) — Anti-globalization activists rioted violently for a second night as Hamburg hosted Group of 20 leaders, setting up street barricades, looting supermarkets and attacking police with slingshots and firebombs on Saturday.

Police said riots were extremely aggressive in the early hours of Saturday in the city's Schanzenviertel neighborhood, which is only a few hundred meters (yards) away from the summit grounds. Hundreds of officers went into buildings to arrest rioters wearing black masks from rooftops while being attacked with iron rods and Molotov cocktails. Thirteen activists were arrested when special units stormed one building.

About 500 people looted a supermarket in the neighborhood as well as smaller stores. Cars were torched and street fires lit as activists built barricades with garbage cans and bikes.

World leaders have come together in the northern German port city for two days to tackle contentious issues including terrorism, climate change and trade.

Most protesters expressed their opposition to the summit in peaceful ways, asking for quick action on climate change and solutions to the migration crisis. But a few thousand rioters, some of them from abroad, created havoc in the city. They've battled riot police for two consecutive days, expressing rage against capitalism and globalization and called for open borders to let all refugees enter Europe. Their anger is not so much focused against President Donald Trump or other leaders, but directed against police as symbols of authority.

Police arrested 114 people, and 89 activists were temporarily detained. More than 200 officers have been injured since the start of the protests Thursday night.

Even one of the organizers of the more radical leftist protests distanced himself from the overnight riots in Schanzenviertel.

"We have the impression that ... some kind of militancy was taken to the streets, that people get a high on it," Andreas Blechschmidt, of the alternative culture center Rote Flora at Schanzenviertel, told public broadcaster NDR. "We think that's politically and substantially wrong."

Police called on witnesses of the riots to upload photos and video footage on their server to help with the investigation and prosecution of violent activists.

On Saturday morning, city cleaners took to the streets sweeping up rubble and using heavy construction equipment to haul away the leftovers of last night's barricades and fires, while in other parts of Hamburg, peaceful protesters started new marches holding up red balloons and dancing through the streets to live music.

Activists from the environmental Greenpeace group scaled a bridge and unfurled a banner saying, "G-20: End Coal."

The group said in a statement that 65 activists participated in the protest demanding that G-20 leaders act quickly to phase out coal and speed up global climate action.

Fighting global warming is one of the major issues on the G-20 agenda, but negotiations are proving to be difficult since the U.S. left the international Paris climate agreement a few weeks ago.

"The millions of people threatened by climate change or already suffering its impact expect the G-20 leaders to accelerate their efforts to reduce their emissions," Greenpeace's Susanne Neubronner said. "This can only be achieved by ending the age of coal by a socially just phase-out."

Kirsten Grieshaber contributed to this report from Berlin.