The truce, reached after a dinner of more than two hours, buys time for the two countries to work out their differences in a dispute over Beijing's aggressive drive to supplant US technological dominance.
The wording on climate change was "a little bit more than the status quo but not backtracking", one European Union official said.
Applause broke out in the convention center hall as the leaders, including Trump, signed off on the statement at the end of the two-day summit in the Argentine capital, the first time it has been held in South America.
The United States is unhappy with what it says is the WTO's failure to hold Beijing to account for not opening up its economy as envisioned when China joined the body in 2001. And Beijing agreed to reconsider a takeover by USA chipmaker Qualcomm that it had previously blocked.
Playing down domestic concerns of any compromise by China giving in to Trump's demands, it said "the Chinese public needs to keep in mind that China-US trade negotiations fluctuate".
The two sides also agreed to enhance cooperation on law enforcement and combating illicit drugs, including the synthetic drug fentanyl, Wang said. "This changes the tone and direction of the bilateral conversation".
Trump and Xi were set to talk over dinner Saturday at a summit of world leaders in Argentina. He also canceled a Saturday news conference following the death of former President George H.W. Bush.
At the same time, US farmers have been hurt by reduced Chinese imports of soybeans and other products. If they fail to reach a deal, the 10% tariffs will rise to 25%.
Trump, who has already slapped $250 billion in tariffs on China and threatened more to come next month, sounded upbeat about making progress with Xi.
Trump struck a positive note as he sat across from Xi, despite the US president's earlier threats to impose new tariffs on Chinese imports.
The differences laid bare in Buenos Aires came a day before United Nations climate talks were to get underway on the other side of the world in the Polish city of Katowice.
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Beijing meanwhile has accused the USA of starting "the largest trade war in economic history".
However, tensions still pivoted around the meeting between Trump and Xi over trade. It also notes a recent United Nations report that warned damage from global warming will be much worse than previously feared, and expresses support for an upcoming United Nations climate meeting in Poland meant to nail down how countries will meet promises made in the Paris accord.
China nixed the proposed takeover earlier this year, citing antitrust concerns, after US and European regulators approved the deal.
On the U.S. side, these included advisers such as Kudlow and Treasury Secretary Steven Mnuchin, who are widely seen as wanting to cut a deal, but also hawkish advisers like Peter Navarro and United States trade representative Robert Lighthizer.
A stronger USA and China would only make the world even stronger and more prosperous.
Earlier that day, Trump signed a revamped three-way trade deal with Canada and Mexico, fulfilling a longstanding pledge, though the agreement could face headwinds in Congress. "During the past 40 years, with the support of the worldwide community, we in China have forged ahead with perseverance and made historic achievements in development", said Xi.
China and the United States have agreed to halt additional tariffs as both countries engage in new trade negotiations with the goal of reaching an agreement within 90 days, the White House said on Saturday.
Beijing hopes to persuade Trump to abandon plans to hike tariffs on $200 billion United States of Chinese goods to 25 per cent in January, from 10 per cent at present.
For American farmers, who have suffered since President Donald Trump unleashed tariffs on China, and Beijing hit back with its own tariffs, mostly on American agricultural products, the truce is light at the end of a tunnel of falling profits. The commitments by the communist regime fell short of the key structural reforms that Washington has been demanding, such as ending intellectual property theft and forced technology transfer. Trump now says he'll hold back on those tariff hikes for 90 days, as US and Chinese negotiators work on terms of a deal.
There was an implicit contrast in some of the tributes offered at the Buenos Aires summit between Bush and the current White House occupant, Donald Trump, whose disruptive brand of diplomacy has stoked the deepest divisions in the G20's 10-year history.
Both agreed that "great progress" has been made on North Korea, and that both Trump and Xi would strive, along with North Korean Chairman Kim Jong Un, to "see a nuclear free Korean Peninsula".