Without mentioning President-elect Donald Trump's name, Chinese President Xi Jinping appeared to signal his concern that Trump's protectionist rhetoric on the campaign trail could send the U.S.-China relationship into another valley.

China's President Xi Jinping told his U.S. counterpart Joe Biden that the issues of Taiwan, democracy, human rights and rights to development are "red lines" for China and not to be challenged, the official state media Xinhua said on Sunday.

President Joe Biden and his Chinese counterpart, Xi Jinping, closed the book on their diplomatic relationship Saturday, meeting for a final time amid uncertainty over what the next Donald Trump presidency might portend for their two countries’ ties.