The world's deepest underwater sinkhole in South China Sea has been stumbled upon by scientists, according to China's state broadcaster CCTV.

For a year, experts have been researching the site. They call this the "Dragon Hole" going by local parlance. It is 987 feet (300 meters) deep. Scientists from the Sansha Ship Course Research Institute for Coral Protection used an underwater robot with a depth sensor to determine the size of the sinkhole. 

While experts have discovered over 20 species of fish in the higher reaches of the sinkhole, also called a blue hole, it is seen to be free of oxygen below 100 meters, so life is not likely to survive in that region.

A large sinkhole or cave system in the ocean visible from the surface is called a "blue hole". The hole is described by locals as the "eye" of the South China Sea. It is situated in a coral reef slightly away from the Paracel Islands.

Earlier, it was Dean's Blue Hole in the Bahamas that was thought to be the "world's deepest underwater sinkhole," at below 660 feet.

The Sansha city government in Hainan Province, China, agreed that it has devised a number of ways that it can protect and research the blue hole in the South China Sea.