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 the search for alternative clean energy sources.

Started on 10th May, the mining operation in waters near the Pearl River estuary has exceeded 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 metres of gas, mainly methane, with an average daily extraction of more than 5,000 cubic metres of high-purity gas, and the highest daily output of 35,000 cubic metres, the bureau said in a statement carried by state news agency Xinhua.

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 18th May. Such ice usually exists in seabed or tundra areas with strong pressure and low temperature necessary for its stability.

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

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

The China Geological Survey Bureau's Deputy Director, Li Jinfa, said combustible ice will play a vital role in China's energy security and economic development. "It is considered a strategic alternative to oil and natural gas in the future. Not just China, the world at large sets its eyes on it," he said.

He added that other countries, such as Japan, had also begun mining combustible ice, but operations were suspended due to a significant amount of sand entering the production wells. This time, however, Chinese scientists invented a new technique to prevent sand from disrupting the exploration. Other adjustments were also made to ensure commercial explorations.

Environmental tests neither showed methane leaks nor geological hazards.

China began research in combustible ice in 1998. The latest exploration has showcased a number of breakthroughs.

"China is leading the world in combustible ice exploration, whether it is about theory, techniques, machinery, or engineering. The trial will have a big impact on the world's energy sector," said Ye Jianliang, Director of the Guangzhou Marine Geological Bureau.

Li said his bureau will double its efforts on research to prepare for the commercial production of combustible ice, with emphasis on ocean ecology protection and "green" exploitation of the new energy. Regulations on exploitation management and industrial policy are also being drawn up.