Google, BMW, Volvo and Samsung SDI are the first global companies to have signed up to a World Wildlife Fund (WWF) call for a moratorium on deep-sea mining, the WWF said on Wednesday.

In backing the call, the companies commit not to source any minerals from the seabed, to exclude such minerals from their supply chains, and not to finance deep seabed mining activities, the WWF said in a statement.

Deep-sea mining would extract cobalt, copper, nickel, and manganese - key materials commonly used to make batteries - from potato-sized nodules which pepper the sea floor at depths of 4-6 kilometres and are particularly abundant in the Clarion-Clipperton Zone in the North Pacific Ocean, a vast area spanning millions of kilometres between Hawaii and Mexico.

"With much of the deep sea ecosystem yet to be explored and understood, such activity would be recklessly short-sighted," WWF said in a statement.

The moratorium calls for a ban on deep seabed mining activities until the risks are fully understood and all alternatives are exhausted.

BMW said raw materials from deep-sea mining are "not an option" for the company at present because there are insufficient scientific findings to be able to assess the environmental risks. Google and Volvo did not immediately respond to emailed requests for comment.

South Korea's Samsung SDI said it was the first battery maker to participate in WWF's initiative.

In the meantime, deep-sea mining companies are pushing ahead with preparatory work and research on seabed licence areas.

Companies that hold exploration licences for swathes of the sea floor, including DeepGreen, GSR and UK Seabed Resources - a subsidiary of Lockheed Martin's UK-based arm - hope to eventually sell minerals from the seabed to carmakers and battery companies.

DeepGreen, which recently announced plans to go public in a merger with a special purpose acquisition company (SPAC), has previously said seabed mining will be more sustainable than mining on land because it creates less waste and the nodules containing minerals have higher concentrations of metals than deposits found on land.

Meanwhile Norway has said it could license companies for deep-sea mining as early as 2023, potentially placing it among the first countries to harvest seabed metals. 

(Reporting by Helen Reid; Editing by Amran Abocar and Kenneth Maxwell) ((Helen.Reid@thomsonreuters.com; +27 66 156 5214;))