The Group of 20 summit is under way in this northern German city amid violent street protests outside and tensions inside the venue over trade issues and climate change.
Meanwhile, U.S. President Donald Trump and Russian President Vladimir Putin planned to have their first face-to-face sit-down talks on the sidelines of the summit on the afternoon of July 7.
"I look forward to all meetings today with world leaders, including my meeting with Vladimir Putin. Much to discuss," Trump said on Twitter on July 7.
Kremlin spokesman Dmitry Peskov said later that Trump and Putin had exchanged a handshake and would "meet separately and see each other soon."
German Chancellor Angela Merkel’s official welcome to leaders of major industrialized countries came as some protesters attacked a police station, torched police cars, and attacked security at a hotel where Putin and other foreign leaders were staying.
Hamburg police said a demonstrator also fired a flare gun at a police helicopter, narrowly missing the aircraft.