China has explored about 210,000 cubic meters of the combustible ice in the South China Sea and the tests are proceeding smoothly, a local geological bureau said on Saturday.

A month has passed since the test on the extraction of combustible ice started in waters near the Pearl River estuary, said Guangzhou Marine Geological Bureau.

By Saturday afternoon, its daily production is 6,800 cubic meters, the bureau said.

"The process of gas production is smooth, and we are laying foundation for the next step," the statement said.

Combustible ice usually exists in seabed or tundra areas, which have the strong pressure and low temperature necessary for its stability. It can be ignited like solid ethanol, which is why it is called "combustible ice."

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

Ye Jianliang, head of the bureau, said strict measures have been taken to protect the environment.

"We are monitoring the air, sea water, seabed and the exploration equipment. We also closely follow the amount of methane and carbon dioxide," he said, adding that no pollution to the environment or geological hazards had happened so far.