"As a result of these very productive talks, I will be delaying the US increase in tariffs now scheduled for March 1", the president wrote.
Negotiators have struggled this week to overcome differences on specific language to address tough USA demands for structural changes in China's economy, two sources familiar with the talks said.
"We can't be sure whether this constitutes a major cave or success because we don't know the details of what has been negotiated".
Trump tweeted on Sunday night that progress had been made on "structural issues including intellectual property protection, technology transfer, agriculture, services, currency, and many other issues" in the talks in Washington.
The official Xinhua news agency used nearly the exact same language, reporting "substantial progress" on those thorny issues in the talks led by Xi's top trade negotiator, Vice Premier Liu He.
In retrospect, the bilateral meetings in Beijing prior to last week's talks in Washington were "critically important", he said.
The delay in tariffs on $200bn worth of Chinese goods was the clearest sign yet of a breakthrough the two sides have sought since calling a 90-day truce in a trade war a year ago.
Recent tariffs imposed by the Trump administration have cost USA businesses 2.7 billion US dollars in November 2018 alone, according to data released by Tariffs Hurt the Heartland, a campaign backed by the Washington-based National Retail Federation (NRF), the world's largest retail trade association.
EU Brexit negotiator says United Kingdom 'decision more important than extra time'
Goldman raised the probability of that outcome to 55% from 50% while cutting its view of no-deal Brexit to 10% from 15%. French President Emmanuel Macron said any such request would need to be justified by "a clear perspective on the goal".
Trump had threatened a 10 percent to 25 percent increase in tariffs on $200 billion worth of Chinese exports, The Associated Press reported.
The two sides are working on a text that could top 100 pages, a person tracking the talks said.
It's better than the alternative, which is to make production practically impossible here in the USA via the Green New Deal, incentivizing factories and growth elsewhere including China and making Americans even more dependent on imports.
"If all works well we're going to have some very big news over the next week or two", he said, though he took care to add that "we still have a little ways to go".
The trade war was started by Trump over claims of unfair trading practices and intellectual property theft by the Chinese.
"Trump has now substantially ratcheted up the pressure on his negotiators to strike a deal with China, even if it does little to assuage US hard-liners' concerns about China's commitments on core structural issues", Cornell University Professor Eswar Prasad told the Wall Street Journal.
Beijing has reportedly proposed a significant increase in its imports of U.S. energy and agricultural exports.
Sources told CNBC on Friday that China had committed to buying up to $1.2tn in United States goods, but there had been no progress on the intellectual property issues.
The discussions began with a photo opportunity where U.S. Trade Representative Robert Lighthizer and Chinese Vice Premier Liu He faced each other silently across a table in the Eisenhower Executive Office Building next door to the White House. Europe, Japan and other trading partners echo US complaints those violate Beijing's free-trade obligations.