The mining of combustible ice, a natural gas hydrate, is underway in the Shenhu area of the South China Sea on July 9, 2017. [Photo/Xinhua]

GUANGZHOU - China on Sunday completed a 60-day trial of mining gas hydrates, commonly known as combustible ice, in the South China Sea, marking breakthroughs in human's search for alternative clean energy sources.

Started from May 10, the mining operation in waters near the Pearl River estuary has beaten previous expectations and set world records in both the length and total amount of extraction, according to the China Geological Survey Bureau.

The trial exploration produced over 300,000 cubic meters of gas - mainly methane, with an average daily extraction of more than 5,000 cubic meters of high purity gas, and a highest daily output of 35,000 cubic meters, said the bureau.

Meanwhile, 6.47 million sets of experimental data were recorded.

China declared its first success in collecting samples of combustible ice in the South China Sea on May 18, which usually exists in seabed or tundra areas with the strong pressure and low temperature necessary for its stability.

The substance can be ignited like solid ethanol, which is why it is called combustible or flammable ice.

One cubic meter of combustible ice, a kind of natural gas hydrate, is equal to 164 cubic meters of regular natural gas.

China Geological Survey Bureau's deputy director Li Jinfa said combustible ice will play a vital part in China's energy security and economic development.

"It is considered a strategic alternative to oil and natural gas in the future," Li said. "Not just China, the world at large sets eyes on it."

He said other countries like Japan had also begun mining combustible ice, but operations were suspended due to a significant amount of sand entering the production wells.