China's role in upholding multilateralism is fundamental, United Nations Secretary-General Antonio Guterres told President Xi Jinping on the sidelines of a security forum meeting on Saturday.

Xi in turn said China would always be a "reliable partner" to the United Nations and continue to provide "stability and certainty".

Guterres is in China's northern port city of Tianjin for a meeting of the Shanghai Cooperation Organization, where Russian President Vladimir Putin and leaders from Central Asia, Southeast Asia, South Asia and the Middle East will gather.

"In this moment in which multilateralism is under fire, the support of China... is an extremely important element to preserve," Guterres said.

"We see new forms of policy that are sometimes difficult to understand, that sometimes look more like a show than the serious diplomatic efforts and in which business and politics seem sometimes also mixed.

"The role of the People's Republic of China as a fundamental pillar of the multilateral system is extremely important and we are extremely appreciative and grateful for that."

President Xi reiterated his support by telling the UN chief: "China is willing to deepen cooperation with the United Nations, supports its central role in international affairs, and jointly shoulder its responsibilities in maintaining world peace and promoting development and prosperity." (Reuters)