A deep-sea mining robot being tested on the Pacific Ocean floor at a depth of more than four-kilometres has become detached from its cable.
A Belgian company, Global Sea Mineral Resources, has been trialling a robot prototype, Patania II, in the Clarion-Clipperton Zone, which lies between Hawaii and Mexico.
The machine is meant to collect the potato-sized nodules rich in cobalt, and other metals used in batteries, that pepper the seabed in this area.
It was connected to a ship with a five-kilometre cable, but the company says it has come free and is now resting on the seafloor.
An operation to reconnect it is under way.
Several Pacific Island states, including the Cook Islands, Tonga, Kiribati and Nauru, are backing exploration efforts in their marine environments.
But critics, including the environmentalist David Attenborough, say deep-sea mining is untested and has a largely unknown environmental impact.
Companies that might use the minerals collected, including Google, BMW, AB Volvo, and Samsung SDI, have backed a call for a moratorium on it.
Global Sea Mineral Resources' trial is being observed by independent scientists from 29 European institutes who will analyse data and samples collected by the robot in order to measure the environmental effects.
Global Sea Mineral Resources has said it will only apply for a mining contract if the science shows that deep seabed minerals have advantages, from an environmental and social perspective, over relying solely on land-based mining.