US President Donald Trump, who is attending his first G20 and is a maverick on numerous summit's issues, has called on China to "end this nonsense once and for all".
German Chancellor Angela Merkel says Berlin can no longer rely on the U.S. when it comes to the United Nations, the Middle East, or European security.
It pledges support for North Atlantic Treaty Organisation but says that Europe has to take greater responsibility for its own defense.
Police uses a water cannon during a protest at Schanzenviertel ahead the G20 summit in Hamburg, Germany, July 4, 2017. It scraps the 2013 pledge to strengthen economic ties with the USA, and pledges to "reinvigorate the relationship with France", whose new president, Emmanuel Macron, has been critical of Trump.
The chancellor instead reaffirmed her claim as she prepares to host Trump at the G-20 summit in Hamburg, Germany this weekend.
It is estimated that on the second day of the summit, about 100 thousand protesters will take part, including the representatives of organizations for the protection of the environment and consumer rights, trade unions, human rights activists, right-wing extremists, and leftists.
"If we simply try to carry on as we have in the past, the worldwide developments will definitely not be sustainable and inclusive", she said.
China's Most Important Partner Within EU – Chinese Premier
Interior Minister Thomas de Maiziere, in the Sunday edition of the daily Bild, warned that any violence "should be nipped in the bud".
"Where they have commonality would be on economic growth", he said.
A police spokesman quoted by the AFP news agency put the turnout at the protest at around 10,000, while the organisers said the figure was far higher.
Without mentioning the protests that have German security officials anxious about possible acts of sabotage this week in the country's second-largest city, Merkel noted that these non-traditional issues were forced onto the G20 agenda.
Trump has said he will pull the United States out of the 2015 Paris deal on tackling climate change.
At least 15,000 police officers from all of Germany's the federal states are being deployed to ensure public security at the G20 summit.
The two leaders have also clashed over Trump's decision to withdraw from the Paris Climate Agreement.