The U.S. has come to a “very substantial phase one deal” with China in the high-stakes trade negotiations between the two economic superpowers, President Donald Trump says Friday.

“Phase two will start almost immediately” after the first phase is signed, Trump says in the Oval Office alongside Chinese Vice Premier Liu He.

Both sides in the long-running talks, which resumed at the top level this week, signal optimism.

The U.S. has come to a “very substantial phase one deal” with China in the high-stakes trade negotiations between the two economic superpowers, President Donald Trump said Friday.

“Phase two will start almost immediately” after the first phase is signed, Trump said in the Oval Office alongside Chinese Vice Premier Liu He.

The first portion of the trade deal will be written over the next three weeks, Trump said. It will address intellectual property and financial services concerns, along with purchases of about $40 billion to $50 billion worth of agricultural products by China, Trump said.

It’s a “tremendous deal for the farmers,” Trump said.

Asked what changed between these trade negotiations and prior discussions - talks broke down in May, for instance, leading to a sharp rise in tensions and the imposition of tariffs on billions of dollars worth of goods -Trump said it’s because this deal is “bigger.”

Liu, asked the same question by CNBC, summed up the difference as “cooperation.”

Treasury Secretary Steven Mnuchin also announced in the Oval Office that the White House has scrapped a new round of tariffs on imports of Chinese goods, which were set to go into effect Oct. 15.

“We have a fundamental understanding of the key issues, but there is more work to do,” Mnuchin said, CNBC’s Eamon Javers reported.

Mnuchin said the U.S. will even be evaluating whether to rescind its decision in August to designate China a “currency manipulator.”

“We’ve made a lot of progress over the last two days,” Mnuchin said.

Both sides in the long-running talks, which resumed at the top level this week, have signaled optimism about coming to an agreement of some sort in the near future.

The Dow Jones Industrial Average jumped more than 300 points on the day.

Earlier Friday, Trump said in a tweet that Washington and Beijing are sharing “warmer feelings” during this round of talks than in the “recent past.”

The president later assured that “When the deal is fully negotiated, I sign it myself on behalf of our Country. Fast and Clean!”

David Dollar, a senior fellow at the Brookings Institution, told CNBC that “the two sides are not discussing a trade treaty that requires congressional approval.”

“It is a more informal agreement in which China will undertake to do certain things such as buy U.S. agricultural products and the administration will undertake not to follow through with the next rounds of tariffs. Since those tariffs do not require congressional approval, the administration can postpone or cancel without that approval,” Dollar said.