China and the United states should boost macroeconomic policy coordination and jointly contribute to a recovery of confidence on global markets, Chinese Vice President Xi Jinping told U.S. Vice President Joe Biden who is on a trust-building visit in Beijing. "Turmoil on international financial markets has deepened recently and global economic growth is facing severe challenges," the Chinese government’s website quotes Xi, who is expected to succeed Hu Jintao as president from early 2013, as saying. "As the world's two biggest economies, China and the United States have a responsibility to strengthen macroconomic policy coordination and together boost market confidence." Biden said strategic confidence was a key factor to develop long-term stable Sino-American relations, calling for closer ties with China. The two nation’s relations are far-reaching, both being the world’s largest economies and key trade partners for each other. They are also often strained by quarrels over currency policy, U.S. arms sales to Taiwan, diplomatic disputes from Sudan to North Korea, and over human rights.