Gas has started flowing to energy-hungry China through a pipeline from Myanmar, Beijing's official media reported, in a major project that highlights their economic links even as political ties weaken.
The 793-kilometre (492-mile) pipeline runs from Kyaukpyu on Myanmar's west coast, close to the offshore Shwe gasfields, and across the country.
It enters southwest China at Ruili, near areas where heavy clashes between the rebel Kachin Independence Army and the Myanmar military were reported earlier this year.
As well as diversifying China's sources of fuel, by supplying energy to the vast and economically less developed west it could help Beijing's attempts to promote growth there.
The pipeline has been years in construction and went into operation on Sunday at a ceremony in Mandalay, the official Xinhua news agency reported.
"When torches flamed in the sky, a storm of applause and cheers broke out," it said.
In an editorial on Monday the Global Times newspaper, affiliated with the ruling Communist Party, said: "This is another breakthrough in China's strategy of energy diversification and has obvious significance in reducing China's dependence on the Strait of Malacca for the import of oil and natural gas."
A parallel oil pipeline is also part of the project, with the China National Petroleum Corporation (CNPN) the major partner in both assets.
According to Xinhua, the gas pipeline will be able to carry 12 billion cubic metres annually, while the crude oil pipeline has a capacity of 22 million tonnes per year.
The start of the project comes as resource-rich Myanmar shakes off decades of rule by generals who kept the country largely isolated from the rest of the world.
They did, however, maintain close economic links with China, which for years was the major foreign influence in a country that was under heavy international sanctions.
Now, with Myanmar opening up politically and economically, more countries are setting up operations and seeking deals which sanctions had prevented.
"Myanmar used to be sanctioned by the West and China was its only friend," the Global Times editorial acknowledged. "Nowadays, it has opened more to the West. This will reduce its passion in cooperating with China, but does not mean it will set itself against China."
But in a warning that Beijing expects its economic interests to be protected, the newspaper cautioned Myanmar that it must ensure agreements regarding the project are fulfilled, no matter who eventually leads the country.
"China should be determined to supervise Myanmar in doing so," the paper said. "Myanmar should hold a serious attitude toward China, and Chinese will take (the Myanmar) people's attitude toward the pipeline as a test of their stance on China."