China is expanding its fleet of coral-monitoring submersibles and plans to build larger models that could also be used for reconnaissance purposes.
The soft-body submersibles are designed to resemble manta rays and move in similar ways.
The earlier versions, some of which were painted to resemble cartoon characters, were small and lightweight and designed to monitor coral reefs, but state broadcaster CCTV's military channels said the size and scope of the devices would be expanded.
"This year, we are preparing to carry out deep-sea applications of 800kg [1,765 pounds] class [submersibles]," Cao Yong, a professor at Northwestern Polytechnical University told CCTV.
He added: "We will even develop a tonne-class prototype in the future, which can carry more powerful payloads and sail farther, including … future integrated reconnaissance and strike [roles]."
Cao's team began developing a submersible for coral reef monitoring in 2006, studying the swimming patterns of marine organisms for their prototypes, the report said.
They successfully began monitoring marine life in the South China Sea earlier this year, monitoring outbreaks of species such as the crown-of-thorns starfish, which threaten coral reefs by feeding on them.
The team's smaller submersibles can be used for marine education and coral reef monitoring, while their larger models can dive deeper and longer to collect more data, according to CCTV.
Each submersible has space for additional equipment, but the team is planning to deploy them in groups next year to maximise their benefits.
"The endurance, load capacity, and range of a single unit are all very limited. If we form a cluster, we can travel longer distances," Hao Yiwei, a researcher at Northwestern Polytechnical University, told CCTV.
China is not the only country testing out manta ray-like submersibles. A similar underwater drone passed in-water tests in the United States earlier this year.
The vessel, made by defence technology company Northrop Grumman, will conduct "long-duration, long-range missions in ocean environments where humans can't go," the company said.
Their autonomous drone can anchor to the sea floor to hibernate in a low power mode, and will also be able to carry payloads for different missions.
The company said that the US Defence Advanced Research Projects Agency, who commissioned the drone, has a "vision of providing groundbreaking technology to create strategic surprise."
China's manta ray submersibles are equipped with cameras, sonar, and the BeiDou navigation system, allowing it to transfer real-time video and positioning information back to the researchers.
Last year one of the vessels was able to reach a depth of 1,000 metres (600ft), according to CCTV.
Cao said the team is not worried the drones will be attacked by sharks, but microorganisms might attach themselves to its surface and impede its navigation.
To get round this problem the team is looking at ways to apply a special gel to "make these microorganisms mistakenly think that this is seawater".