Trump was typically coy on Friday even as he noted some positive signs.
"We're working very hard. If we could make a deal that would be good. I think they want to. I think we’d like to. We’ll see," he said, speaking during a meeting with Japanese Prime Minister Shinzo Abe.
A Chinese foreign ministry official in Buenos Aires said there were signs of increasing consensus ahead of the discussions but that differences persisted.
Beijing hopes to persuade Trump to abandon plans to hike tariffs on $200 billion of Chinese goods to 25 percent in January, from 10 percent at present. Trump has threatened to go ahead with that and possibly add tariffs on $267 billion of imports if there is no progress in the talks.
Trump has long railed against China's trade surplus with the United States and Washington accuses Beijing of not playing fairly on trade. China calls the United States protectionist and has resisted what it views as attempts to intimidate it.
The two countries are also at odds militarily over China’s extensive claims in the South China Sea and U.S. warship movements through the highly sensitive Taiwan Strait.
Xi and leaders from the BRICS group of leading emerging economies - Brazil, Russia, India, China and South Africa - called in a statement on Friday for open international trade and a strengthening of the World Trade Organization (WTO).
Trump cited Russia's seizure of Ukrainian ships last week as the reason he canceled a planned bilateral meeting with Russian President Vladimir Putin.
The presence of Crown Prince Mohammed bin Salman at the summit also raised an awkward dilemma for leaders, and Saudi Arabia's de facto leader cut a lonely figure standing at the edge of the G20 family photo on Friday.
Prince Mohammed arrived under swirling controversy over the murder of Saudi journalist Jamal Khashoggi in the Saudi consulate in Istanbul on Oct. 2. Saudi Arabia has said the prince had no prior knowledge of the murder.
Human Rights Watch asked Argentine prosecutors to investigate him for human rights abuses.
