Police say riots were extremely violent in the early hours of Saturday in the city's Schanzenviertel neighborhood. Hundreds of officers went into buildings to arrest rioters while being attacked with iron rods and Molotov cocktails thrown from the roofs.
Thirteen activists were arrested when special units stormed one building, AP reported.
Some 500 people looted a supermarket in the neighborhood as well as smaller stores. Cars were torched, street fires lit as activists built barricades with garbage cans and bikes.
World leaders will come together later Saturday to tackle issues including terrorism, climate change and trade.
