The United States and China, the world's two largest economies, will see Saturday if they can find a breakthrough to exit a spiraling trade war as their presidents meet at a tense G20 summit. With markets watching nervously, US President Donald Trump has described the Buenos Aires summit of the 20 leading economic powers as a deadline for China to meet his demands or risk even further pressure. The summit itself, with leaders from France, Russia and Saudi Arabia among those attending, has been struggling to carve out any accord on fighting climate change while hot-button disputes such as Ukraine loom large. Trump, who has already slapped $250 billion in tariffs on China, sounded upbeat about making progress with his counterpart Xi Jinping after weeks of dire warnings. "We're working very hard. If we could make a deal, that would be good," Trump told reporters Friday as he met Japanese Prime Minister Shinzo Abe on the first of the summit's two days. "I think they want to, and I think we'd like to. And we'll see," Trump said. Trump has thrown out the traditional US playbook on free trade since his shock 2016 election, vowing to protect forgotten workers and put "America First." Xi has in turn cast himself as a defender of stable global capitalism, a startling transformation for the leader of a communist state whose entry into the World Trade Organization less than two decades ago was controversial. In a speech to fellow G20 leaders, Xi said that the major economies "should firmly uphold free trade and the rules-based multilateral trading system." But in a rhetorical olive branch to Trump, Xi pledged to do more to open up China's economy. "China will continue to deepen market-oriented reform, protect property rights and intellectual property rights, encourage fair competition and do more to expand imports," he said. Trump has accused China of rampant theft of US technology and demanded that the emerging power end its requirements that foreign companies team up with local partners. In the run-up to November 6 congressional elections, Trump ramped up criticism and accused China of interfering domestically to hurt his Republican Party. But tensions have eased since then, with Secretary of State Mike Pompeo assuring that the United States is not seeking a new Cold War and US and Chinese trade officials swapping a lengthy list of items up for discussion. Trump's criticisms of China's trade policy enjoy wide support across the US political spectrum, but some fear that the president has bitten off more than he can chew with a go-it-alone campaign that could damage markets worldwide. Trump counted a victory Friday for his brash trade stance as the United States, Canada and Mexico signed a new trade deal, a successor to the North American Free Trade Agreement. While short of a complete rewrite of NAFTA once promised by Trump, he hailed the new United States-Mexico-Canada-Agreement as an "incredible milestone." He secured the support for the new agreement both of Prime Minister Justin Trudeau and Mexico's incoming leftist president, Andres Manuel Lopez Obrador. The state-run China Daily said that the Pacific powers could strike a deal in Buenos Aires but warned the United States against pushing too hard on technology. "Should there be any other aspirations, such as taking advantage of the trade spat to throttle Chinese growth, then an agreement is unlikely to be reached," the newspaper said in an editorial Friday. "But a good deal means both sides walking away happy. The US should give its habitual winner-take-all approach to international relations the weekend off," it said. Read also: G20 summit: India, Russia, China hold trilateral after 12 years; call for reforming multilateral institutions A substantive deal between the United States and China could mark a major feat for the G20 summit, where expectations for collective action have been low. With Trump feuding with close US allies, two major summits this year - the Group of Seven democracies and the Asia-Pacific Economic Cooperation forum - ended without once-routine statements. A French source said that European leaders were trying to forge a statement on climate change even without the United States. Trump has decided to pull the United States from the Paris accord on curbing carbon emissions, saying it is unfair, despite mounting evidence of the changing climate's dire effects. Trump called off talks with Russian President Vladimir Putin at the summit, officially due to outrage over Moscow's naval skirmishes with Ukraine. But Trump is also under mounting pressure at home in an investigation over whether his presidential campaign colluded with Russia - a topic sure to dominate his press conference shortly before he meets Xi over dinner.