US and Chinese negotiators have spoken on the phone, continuing discussions to end a trade battle between the world’s two largest economies that has upended global supply chains and roiled financial markets.

US Trade Representative Robert Lighthizer and Treasury Secretary Steven Mnuchin spoke with Chinese Vice Premier Liu He and Minister Zhong Shan on Tuesday to continue negotiations to resolve outstanding trade disputes between the countries, a US official said in an emailed statement.

“Both sides will continue these talks as appropriate,” the official said in an email, declining to provide details on what was discussed and the next steps for talks.

The negotiations pick up after a two-month hiatus but it’s been a year since a tit-for-tat tariff battle began between the two countries. Washington wants Beijing to address what US officials see as decades of unfair and illegal trading practices.

Washington and China agreed during a Group of 20 nations summit in Japan last month to resume discussions, easing fears of an escalation.

After meeting with Chinese President Xi Jinping at the G20, US President Donald Trump agreed to suspend a new round of tariffs on $US300 billion worth of imported Chinese consumer goods while the two sides resumed negotiations.

Trump said then that China would restart large purchases of US agricultural commodities, and the US would ease some export restrictions on Chinese telecom equipment giant Huawei Technologies.

Earlier on Tuesday, White House economic adviser Larry Kudlow said China was expected to move forward “quickly” with agricultural purchases from the US. He also said relaxed US government restrictions on Huawei could help the technology giant but would only be in place for a limited time.

“President Xi is expected, we hope in return for our accommodations, to move immediately, quickly, while the talks are going on, on the agriculture (purchases),” Kudlow said at an event hosted by CNBC. “That’s very, very important.”

Kudlow, the director of the White House’s National Economic Council, later told reporters there was no specific timeline for the agricultural buys, or for reaching an agreement. “No timeline. Quality not speed,” he added.

Three sources familiar with the state of the talks said the Chinese side did not make firm commitments for immediate purchases. It’s unclear that the two sides’ differences have narrowed, even as the discussions resume.

Meanwhile the Trump administration will exempt 110 Chinese products, from medical equipment to key capacitors, from hefty tariffs, it said on Tuesday, offering relief to some US firms which have said the taxes harm their bottomlines.

The relatively narrow exemption list will provide relief from 25 per cent tariffs the US slapped on $US34 billion of Chinese imports on July 6, 2018. The retroactive exclusions are effective as of that date, and extend for a year from Tuesday.

The waivers by the US Trade Representative’s office follow another 1000 exemptions granted in the past year.