Three unmanned deep sea devices descended over 10,000 meters underwater and completed sea tests in the Pacific, said Chinese scientists leading the research.

Cui Weicheng, director of Hadal Life Science Research Center at Shanghai Ocean University, led a team of researchers to carry out research at the Challenger Deep in the Mariana Trench, the deepest part of the world's ocean.

The group left Dec. 3 on Zhang Jian, a research vessel and mothership of the Rainbow Fish series, and included three deep-sea landing devices, one unmanned search submersible and a manned submersible, all capable of diving 10,000 meters.

From Dec. 25-27, three deep-sea landing devices descended into the trench, Cui told Xinhua.

The first Rainbow Fish landing device took photographs, the second took sediment samples and the third took biological samples, Cui said.

All three submersibles reached over 10,000 meters, and the third device brought back 103 amphipods, he said.

The Rainbow Fish project is a mobile lab co-funded by the state and private capital.

"The successful sea test marks another step in China's deep-sea research," Cui said.

Globally, there are 26 hadal trenches, defined as those with depths of 6,500 meters or more. They are home to many unknown species as well as energy and metal resources.

In August, China's unmanned submersible "Haidou-1" dived to a depth of 10,767 meters at the Mariana Trench, setting a new Chinese record.

China became the third country after Japan and the United States to build submersibles capable of reaching depths in excess of 10,000 meters.

Scientists forecast China will have a manned submersible capable of descending to 10,000 meters by 2019 or 2020.