"The US authorisation... violates international law and harms the overall interests of the international community," Chinese foreign ministry spokesman Guo Jiakun said.

President Donald Trump on Thursday signed an executive order to "expedite the process for reviewing and issuing seabed mineral exploration licenses and commercial recovery permits in areas beyond national jurisdiction".

Private companies and governments have long eyed the mineral and metal resources found in stretches of the ocean floor.

But they have mostly held off while waiting for the International Seabed Authority (ISA) regulator to devise rules -- a process that began in the 1990s.

The United States never ratified the agreements that empowered the ISA's jurisdiction and is not a member of the UN-affiliated body.

Trump's order demands Washington become a "global leader" in seabed exploration and "counter China's growing influence over seabed mineral resources".

Beijing, which has so far held off mining in international waters while awaiting ISA rules, warned Trump's orders "once again expose the unilateral approach and hegemonic nature of the United States".