A diving expedition has revealed the South China Sea's Dragon Hole, or Longdong, to be the deepest blue hole in the world.

According to state news service Xinhua, Chinese researchers measured the depth of Longdong at 987 feet, besting the previous record held by Dean's Hole in the Bahamas by 324 feet. The entrance to the Dragon Hole measures 426 feet wide.

Blue holes are ocean sinkholes, named so for their rich, dark blue color accentuated by the lighter hues of the surrounding shallows. The holes form over thousands of years as large deposits of limestone and other carbonate rocks dissolve.

The hole begins as a cave hidden beneath the ocean floor.

"Eventually, the process of dissolution causes the cave to reach very close to the Earth's surface, and if the cave ceiling collapses, a blue hole or sinkhole is formed," Pete van Hengstum, a marine geologist at Texas A&M University at Galveston, told Live Science.

Scientists with the Sansha Ship Course Research Institute for Coral Protection didn't dive to the bottom, but sent down VideoRay Pro 4, a remote-controlled submersible with a depth sensor.

In addition to confirming a world record, the researchers and their mini submarine have identified 20 new species of fish living in the blue hole.

Researchers have plans to continue studying the hole and its unique inhabitants.

"We will strive to protect the natural legacy left by the Earth," Xu Zhifei, vice mayor of Sansha City, told Xinhua.