While Mr Xi agreed to buy an unspecified but "very substantial" amount of agricultural, energy, industrial and other products, the White House said.
President Trump and President Xi have agreed to immediately begin negotiations on structural changes with respect to forced technology transfer, intellectual property protection, non-tariff barriers, cyber intrusions and cyber theft, services and agriculture.
Tariffs on $200 billion of Chinese products had been set to jump from 10 percent to 25 percent after January 1, 2019.
The US sent $US10.5 billion worth of new and used cars to China in 2017. Xi also agreed to designate Fentanyl, which has been one of the drugs driving the opioid crisis in the USA, as a Controlled Substance.
Those are "central to Xi's core agenda of making China an innovation superpower", Michael Hirson, Jeffrey Wright and Paul Triolo of Eurasia Group said in a report.
Asia stocks had rallied on the news that Washington and Beijing would not impose any new tariffs during a three-month grace period, during which the two sides are meant to finalize a more detailed agreement. "China will be getting rid of tariffs".
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For example, the Trump administration's concerns about China's alleged theft of US intellectual property remain in place and Beijing's broader push for indigenous advances in its hi-tech sector under the aegis of the "Made in China 2025" initiative have yet to be addressed.
Some lawmakers have criticized Trump for his tough trade talk and actions toward China, including his tariffs and threats of imposing up to $256 billion more in such sanctions if no deal could be reached.
China's decision earlier this year came amid a period of heightening tensions between the US and China over trade and intellectual property issues.
US Trade Representative Robert Lighthizer complained last week China's 40 per cent tariffs on imports of US-made autos are higher than Washington's 27.5 per cent rate for Chinese vehicles and said he was looking at ways to equalise US duties.
The president spoke briefly on Air Force One late Saturday as he left Buenos Aires to return to Washington. The White House's official statement says nothing of the sort; it only says the USA will hold negotiations with China on the latter's "forced technology transfer, intellectual property protection, non-tariff barriers, cyber intrusions and cyber theft, services and agriculture".
Beijing will also begin purchasing agricultural products from United States farmers "immediately". "While we are pleased that American consumers have been protected from additional tariffs on most of our products to date, this announced 90-day reprieve on increased and future tariffs is promising".
Under the agreement, Trump is shelving a plan to raise tariffs on $200 billion worth of Chinese imports from 10 percent to 25 percent from the start of next year - but the hike will kick in if negotiators fail to reach a final deal within 90 days.
Beyond the trade deficit that occupies much of Trump's attention, the US has a long list of grievances it wants to address with Beijing in any upcoming negotiations.
The White House characterized that encounter as an informal chat, but Putin gave it more significance.