German Chancellor Angela Merkel is hoping G20 summit will cement her role as a stateswoman as she seeks re-election in September.
Merkel, who is campaigning for a fourth term, sees the summit, which starts in full on Friday, as a chance for her to polish her diplomatic credentials.
She met US President Donald Trump for an hour on Thursday evening, but less than an hour later police clashed with anti-capitalist demonstrators near the summit venue and fired water cannon at black-clad protesters after they threw bottles.
Before meeting Trump, she struck a consensual tone, holding out hope for agreement on the divisive issue of climate policy and pledging to broker compromises. She vowed to represent German and European interests at the summit but added:
"On the other hand, as hosts we - and I - will do all we can to find compromises."
"There are various options, which can be discussed. We know that the United States have withdrawn (Paris climate accord). All others ... or as far as I know, many many others stand by this agreement," she added.
As summit host, Merkel must seek consensus among the G20 leaders not only on the divisive issue of climate policy but also on trade - an area fraught with risk as Trump pursues his 'America First' agenda.
Indonesian finance minister Sri Mulyani Indrawati said Merkel must be careful not to allow acrimony to undermine the summit.
"There is quite a delicate balance that Angela Merkel will have to navigate in a way, because it is not clear that being confrontational won't just create even more of a credibility problem for G20 cooperation," she said.
She and Trump discussed G20 themes, North Korea, the Middle East, and the conflict in eastern Ukraine, a German government spokesman said. Turkey's Tayyip Erdogan is among other leaders Merkel was to meet.
OECD chief calls for leaders to stick to fighting protectionism
The OECD (Organisation for Economic Cooperation and Development) Secretary General Angel Gurria on Thursday said that international collaboration was the key to success in achieving economic growth, tackling trade protectionism and fighting climate change.
Gurria said the G20 is also guilty of "not resisting protectionist measures" and said. "Well, unfortunately, the G20 has not resisted protectionist measures. Every time we finish one of these meetings, we put out a communique that says that we will resist protectionism, and that we will have a standstill at least for the next two years, and then that we will even roll back some of the protectionist measures. And then we have taken 1,400 protectionist measures since 2008."
"It is about being consistent, about being coherent. If you're saying you are going to fight protectionism, for heaven's sake go and fight protectionism - don't add to it."
Merkel had earlier said she was committed to an open international trading system, despite fears of US protectionism under the Trump administration.
"We're united in our will to strengthen multilateral relations at the G20 summit ... We need an open society, especially open trade flows," Merkel said in Berlin.