US President Donald Trump will have breakfast with Saudi Arabia’s Crown Prince Mohammad bin Salman on Saturday, before meeting Chinese President Xi Jinping.
The two meetings are likely to be the most watched at the four-day summit of the Group of 20 major economies in Osaka, Japan, where trade, regional tension and the looming threat of climate change are on the agenda.
"This will be a difficult G20," Donald Tusk, president of the European Council, said at a meeting with Japanese Prime Minister Shinzo Abe.
"There are global challenges to be met. We need to step up to avoid the climate threats, reform the World Trade Organisation and prepare for the digital revolution."
Mr Abe and French President Emmanuel Macron are expected to lead the charge for action on climate at the summit, but the focus in Osaka is likely to be Mr Trump's meetings with leaders of countries with which the US has continuing disputes.
Mr Trump began with a friendly dinner with Australian Prime Minister Scott Morrison on Thursday after arriving in Osaka amid a tropical storm.
He was scheduled to have breakfast with his host, Mr Abe, on Friday before they are joined by Indian Prime Minister Narendra Modi, after New Delhi recently raised tariffs on nearly 30 US products.
In a tweet on Thursday, Mr Trump called the increase unacceptable and said he would ask Mr Modi to withdraw the tariffs.
Mr Trump's meeting with Russian President Vladimir Putin on Friday afternoon is expected to focus on tension in the Arabian Gulf after attacks on shipping and Iran shooting down a US drone.
They are also expected to discuss the Moscow-backed Syrian regime bombardment of the last rebel stronghold in Syria and fears among US allies in Europe over new Russian nuclear missiles.
Mr Trump has worked closely with Prince Mohammed since taking office. His first overseas visit as president was to the kingdom in 2017.
The White House backed the Saudi leadership's investigation into the killing of journalist Jamal Khashoggi in the kingdom's consulate in Istanbul last year.
It also pushed back against pressure from Congress to end American support for the Arab Coalition fighting Iran-backed rebels in Yemen.
For global markets, investors and businesses, the focus will be on Mr Trump's meeting with Mr Xi, aimed at moving towards a deal to end the US-China trade war.
The US president said on Wednesday that failure to make progress would lead to further substantial increases in tariffs on goods from China.
Mr Trump is set to meet Turkish President Recep Tayyip Erdogan on Saturday, after Ankara announced it would go ahead with plans to buy a Russian anti-aircraft missile system, which the US said would lead to sanctions.
The two leaders have good relations despite differences between their countries on some issues.
Mr Erdogan believed their meeting "will be important for eliminating the deadlock in our relations and strengthening our co-operation", he told the Nikkei newspaper on Thursday.