"The implementation of this project is a bright testament to cooperation between the two countries in the energy sphere," said Turkmen leader Gurbanguly Berdymukhamedov at the vast Galkynysh (Renaissance) gas field that is being jointly developed with China.
"This is the most powerful complex in the region with a capacity of 30 billion cubic meters of gas a year."
Speaking at a gas processing plant in the vast Turkmen desert, Xi added: "This is a successful example of cooperation between China and Turkmenistan in the energy sphere."
The Galkynysh field is estimated to have up to 21.2 trillion cubic metres of gas and more than 300 million tonnes of oil.
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According to British auditors Gaffney, Cline and Associates, it is the second-largest gas field in the world.
Turkmenistan is already exporting gas to China via a pipeline whose first stage was completed in 2009.
Yesterday, Xi and Berdymukhamedov agreed on a range of deals including securing more gas to China which eventually plans to ramp up its gas supplies from Turkmenistan to 65 billion cubic metres annually.