Turkmenistan has agreed to increase its annual natural gas supplies exports to China by 25 billion cubic metres, or a total of 65 billion cubic metres a year.

The arrangement was contained in one of the 14 agreements signed on Wednesday between Turkmenistan's President Gurbanguly Berdymukhamedov and Chinese President Hu Jintao. The deal, however, did not specify the exact date when the gas allocation increment would be implemented.

The increase represents more than half of China's annual natural gas consumption. China, the world's second-largest economy, relies heavily on energy imports to meet its growing demand as well as fuel its economic growth.

Turkmenistan is an energy-rich but isolated ex-Soviet nation. It is believed to have some of the world's biggest gas reserves and is now ranked among the world's fastest-growing economies, where it hopes to gain more economic prosperity from its huge hydrocarbon reserves.

Agreements to loan Turkmenistan to purchase oil and gas equipment, as well as on public security cooperation, anti-money laundering, mutual recognition of academic degrees and anti-terrorism, among others, were also signed by the two leaders, the China Daily reported.

Mr Berdymukhamedov will attend on Thursday the ceremonial opening of a $22 billion pipeline that will carry Turkmen gas to southern China. The 5,370-mile (8,700-kilometre) natural gas pipeline began operating in June, helping boost supplies to the country's booming industrial zones. It is expected to transport up to 30 billion cubic metres of natural gas a year.

President Berdymukhamedov is in China for a four-day visit. It is his third state visit to the Asian country since assuming the presidency in 2007.