US President Donald Trump has signed a trade agreement with China that is expected to boost exports from US farmers and manufacturers, protect American trade secrets, and lower tensions in the two nations’ long-running dispute.

Trump said during a White House ceremony the deal is “righting the wrongs of the past”.

He promoted the signing as a way of delivering economic justice for American workers and said the signing marked “a sea change in international trade”.

The agreement is being described as “phase one” of a larger negotiation focusing on tensions in the US-China trade relationship.

Chinese leader Xi Jinping said in a letter to Trump that the first phase was “good for China, the US and for the whole world”.

The letter was read by Beijing’s chief negotiator, Vice Premier Liu He.

But Wednesday’s agreement left unresolved many of the complaints – notably, the way the Chinese government subsidises its companies – voiced by the Trump administration when it started the trade war by imposing tariffs on Chinese imports in July 2018.

While the deal stops short of many changes the president has sought from China, it leaves in place tariffs on about $US360 billion ($A521 billion) in Chinese imports, leverage the administration hopes will generate future concessions.

US Trade Representative Robert Lighthizer said work on follow-up negotiations will hinge on how China fulfills the commitments it made in the initial phase.

“We have to make sure this is implemented properly,” Lighthizer said.

“This is the first agreement like this of its kind and we have to make sure that it works.”

The White House ceremony gave Trump a chance to cite progress on a top economic priority on the same day the House of Representatives voted to send articles of impeachment to the Senate for a trial.

He told Republican lawmakers attending the ceremony that he understood if they had to leave early for votes.

“They have a hoax going on over there. Let’s take care of it,” Trump said.

The agreement is intended to ease some US economic sanctions on China while Beijing would step up purchases of American farm products and other goods.

Trump cited beef, pork, poultry, seafood, rice and dairy products as examples.

The deal would lower tensions in a trade dispute that has slowed global growth, hurt American manufacturers and weighed on the Chinese economy. Trump said easing trade tensions was critical.

“Keeping these two giant and powerful nations together in harmony is so important for the world,” Trump said. “The world is watching today.”

His Chinese counterpart said “the world is now at a critical historical crossroads”, facing choices of how to promote country-to-country co-operation.

“Co-operation is the only right choice,” Liu said.