ZURICH/WASHINGTON: The United States and China have agreed in principle for their presidents to hold a virtual meeting before year's end, a senior U.S. administration official said on Wednesday, after high-level talks meant to improve communication between the two big powers.

The closed-door meeting at an airport hotel in the Swiss city of Zurich between U.S. national security adviser Jake Sullivan and China's top diplomat, Yang Jiechi, was their first face-to-face encounter since an unusually public and acrid airing of grievances in Alaska in March.

Both sides had described the meeting as a follow-on from President Joe Biden's early September call with Chinese President Xi Jinping, prior to which the world's top two economies appeared to have been locked in a stalemate.

The White House said Sullivan raised concerns about contentious issues such as Chinese actions in the South China Sea, as well as on human rights and Beijing's stances on Hong Kong, Xinjiang and Taiwan.

At the end of the day, however, both Beijing and Washington said the talks, which lasted six hours, were constructive and candid. The U.S. side said the tone was very different from Alaska.

"We do have out of today's conversation an agreement in principle to hold a virtual bilateral (summit) meeting before the end of the year," the U.S. official told reporters.

Asked for further details, White House spokeswoman Jen Psaki said: "We're still working through what that would look like, when and of course the final details we don't quite have them yet."

Biden's call with Xi in September ended a nearly seven-month gap in direct communication between the leaders, and the two discussed the need to ensure that their competition does not veer into conflict.

Biden said on Tuesday that he spoke to Xi about Taiwan and they agreed to abide by the "Taiwan agreement", as tensions ratchet up between Taipei and Beijing.

Taiwan has reported 148 Chinese air force planes in the southern and southwestern part of its air defence zone over a four-day period beginning on Friday, the same day China marked a patriotic holiday, National Day.