Han, the Energy Research Institute's director, told China Daily that the success after 20 years of research and exploration is only a small step in a very long journey.

The potential risks for the environment and technological barriers soften all the optimistic outlooks, he said.

According to Han, collection so far is more of strategic concern with vast uncertainties, and whether the frozen fuel will replace regular oil and natural gas remains to be seen.

Gas hydrate also will face competition from other cleaner alternative fuels, including photovoltaic and wind power. And just like the early days of shale exploration in the United States, successful exploration depends on advanced technologies, reduced costs and environmental risks, he said.

The next step is more of research and trial exploration. Commercial production is unlikely in the next three years, considering storage and transportation costs, potential environmental concerns, the risk of marine pollution and technological barriers.

Being a strong contender to replace regular oil and natural gas, gas hydrate－like any fossil fuel－also raises significant environmental concerns.

According to the US Geological Survey, resources of flammable ice are located at sea bottom, making the collection challenging.

Li said an accident while exploring would lead to a massive leakage of methane gas and intensify the greenhouse effect.

Ye Jianliang, who heads the gas hydrate production field, said strict measures have been taken to protect the environment.

"We are monitoring the air, seawater, seabed and the exploration equipment. We also closely follow the amount of methane and carbon dioxide," he said.

"No pollution to the environment or geological hazards had happened so far."