BEIJING - Amid doubts over the prospects of a harmonious China-US relationship, the world's two largest economies delivered strong messages of cooperation during US Vice-President Joe Biden's visit to Beijing.

"In facing a complicated and fast-changing world, cooperation is the only correct choice for the two countries," Chinese Vice- President Xi Jinping told Biden in their two-hour-long talks on Thursday.

Biden responded by saying, "I am absolutely confident that the economic stability of the world rests in no small part on cooperation between the United States and China."

Biden's six-day official visit to China, which began Wednesday, came on the heels of an unprecedented US credit rating downgrade earlier in August, which created global uncertainty about the safety of dollar assets.

At the end of June, China remained the largest foreign holder of US debt with around $1.165 trillion in US Treasuries.

"As the international financial market has turned increasingly turbulent and global economic growth faces grim challenges, China and the United States, the world's top two economies, have a responsibility to increase macro-economic policy coordination and boost market confidence," Xi said.

"China and the United States are transforming their economic development modes and restructuring their economies, which has provided the two nations with good opportunities for cooperation," Xi added.

However, cooperation between Beijing and Washington has to be based on a solid foundation built with strong mutual trust, which still seems to need be strengthened by both nations.

Over the past 30 years, China has achieved a remarkable economic take-off while being aware of the importance of restructuring its economy. Its rise to the world's second largest economy amid a fledgling global economic recovery has showed the world its unique vitality.

"China's development can be interpreted either as a threat or an opportunity. It depends on the United States' top leadership to make its judgement," said Qu Xing, president of the China Institute for International Studies.

Ni Feng, a Chinese scholar with China's Academy of Social Sciences, said that, as the world's sole superpower, the United States would naturally worry about China's fast growth.

Ni said the vast differences between the two countries' cultural and social patterns would further aggravate that distrust and could very likely to lead to misjudgment.

Only by eliminating distrust can a relationship between China and the US grow in a stable manner, added Ni.

This is why, during his meeting with Biden, the Chinese vice-president urged the two countries to "take an objective and rational view of their respective progress and properly evaluate each other's strategic purpose."

Xi also elaborated on how to build that trust through high-level visits, bilateral dialogue platforms, and exchanges of military and non-governmental sectors.

"The key to ensuring the healthy and steady development of China-US relations is to respect each other's core interests," Xi said.

He said the Chinese people cherish the development path and political system of their own choosing, state sovereignty and territorial integrity.

Taiwan and Tibet-related issues, which concern China's core interests and the feelings of 1.3 billion Chinese, should be handled prudently and properly to avoid damaging China-US relations, he said.

Biden said the United States fully recognizes that issues related to Taiwan and Tibet are part of China's core interests.

He said the United States will firmly stand by the one-China policy and will not support "Taiwan independence," adding that the US fully acknowledges that Tibet is an inalienable part of China.

In a separate meeting with Biden later Thursday, top Chinese legislator Wu Bangguo reaffirmed the importance of building strategic trust and properly dealing with differences and sensitive issues.

Xi stressed that "China and the United States both gain from cooperation and lose from conflicts." Only through cooperation can the two countries forge "a close, permanent and friendly relationship" envisioned by Biden.