President Xi Jinping said on Friday that China wants to reach an initial trade deal with the United States but is "not afraid" to fight back when necessary.

Xi made the remarks two days after US President Donald Trump complained that Beijing had not made sufficient concessions so far, making him reluctant to conclude a bargain.

The world's two biggest economies have been locked in a bruising trade conflict for more than a year, hitting each other with volleys of tariffs on hundreds of billions of dollars worth of goods.

"As we always said we don't want to start the trade war but we are not afraid," Xi told former US officials and other foreign dignitaries at a meeting in Beijing's Great Hall of the People.

"When necessary we will fight back but we have been working actively to try not to have a trade war," he told the group, which included former US secretary of state Henry Kissinger, former US treasury secretary Henry Paulson and former Australian prime minister Kevin Rudd.

Top trade negotiators spoke on the phone on Saturday in what the Chinese commerce ministry described as "constructive" discussions on a preliminary deal.

China has insisted on a rollback of existing tariffs, which Trump said he has not agreed to.

US Congress approval this week of legislation supporting pro-democracy protesters in Hong Kong has also cast a shadow on the negotiations.

"We want to work for a phase-one agreement on the basis of mutual respect and equality," Xi told the foreign visitors, who were in town for the Bloomberg New Economy Forum.