Donald Trump was scheduled to meet with Chinese Vice Premier Liu He at the White House as talks conclude on Thursday.
"They started on a smaller scale", he said, describing the new pledge as "tremendous".
Talks began on the White House campus Wednesday morning with U.S. Trade Representative Robert Lighthizer sitting across the table from Chinese Vice Premier Liu He.
An administration official later clarified the amount as a total of 5 million tonnes, effectively doubling the amount bought by China since resuming limited purchases in December.
During an earlier visit by Liu past year, Trump declined to meet with Xi's close adviser, a slight that irritated Chinese authorities.
"Five million tons of soybeans!".
"That's going to make our farmers very happy."
"At their request, and subject to this deal until March 1st, I'm charging them ten percent on 200 billion", Trump told the outlet when asked about the importance of China implementing intellectual property protections for US investors in China. He also said that the Beijing Winter Olympics is expected to bring China more opportunities in sports cooperation with the global community.
On Wednesday, US intelligence officials told Congress that China is the biggest commercial and military threat to the United States.
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A person familiar with the discussions said a broad range of concerns about access to Chinese agricultural markets were raised in the talks but little progress was made.
As part of the deal, Trump agreed to postpone the planned increase in tariffs on $200 billion worth of Chinese goods. He said a Trump-Xi summit "is, as it has always been, the main event".
Analysts at Capital Economics said: "We think the two countries may just be able to reach a face-saving agreement to tide them over in the short term and avoid an escalation". The two previously met at Mr Trump's Mar-a-Lago resort to discuss trade. Mr. Trump said both sides are "working hard to complete" the deal by that deadline.
It would make "so much sense" for China to "finally do a Real Deal", he wrote on Twitter this month.
If the USA and China reach an agreement on trade, the president told reporters on Thursday, it will be the largest in the world.
Meanwhile, Mr Trump, a self-described "Tariff Man", rejected a previous proposal from Beijing to resolve the dispute with increased purchases of United States goods.
Chinese officials have said their policies do not coerce technology transfers.
But the Chinese side, led by Vice Premier Liu He, would likely have to bring to the table a new offer that goes significantly beyond its previous offers to significantly increase purchases of USA goods, including soybeans, energy and manufactured goods.
The two sides a year ago traded blows, imposing steep tariffs on more than $360 billion in two-way trade, but the United States has more room to manoeuvre in the battle as it buys far more from China than the other way around.