China's President Xi Jinping and Russia's president Vladimir Putin witnessed the signing of a long-delayed $400 billion natural gas deal on Wednesday - after more than ten years of negotiations - at the end of Putin's two-day visit to Shanghai.

The agreement, which involves Russia's top natural gas producer, Gazprom OAO, and China National Petroleum Corp, will supply China with 38 billion cubic meters of gas annually from the eastern gas pipeline for 30 years, starting 2018.

The two sides managed to reach a last-minute agreement on the price - which was the major obstacle for the completion of the deal.

The gas will come from the Kovyktin and Chayandin gas fields in eastern Siberia of Russia and will be piped to China's northeast, the Beijing-Tianjin-Hebei metropolitan area in the north and the Yangtze river delta in the east.

China and Russia have vowed to strengthen cooperation in energy and infrastructure in Russia. According to a joint statement signed by the two leaders after their talks on Tuesday, they will "establish a comprehensive energy cooperation partnership".

CNPC chairman Zhou Jiping, and Wu Xinxiong, head of China's National Energy Administration and deputy head of the National Development and Reform Commission, China's top economic planner, signed the latest deal on the China's behalf.

The successful completion of the deal is based on Russia's strong willingness to find new energy buyers outside of Europe, and also on China's rapidly growing demand for natural gas during the country's energy structure transformation, said Sun Yongxiang, a professor at the Euro-Asian Social Development Research Institute of the State Council's Development Research Center.