UN Secretary-General Antonio Guterres on Monday called the relationship between the two countries "completely dysfunctional".

He said the world's two major economic powers should be cooperating on climate and negotiating more robustly on trade and technology.

Guterres added they should be working together even given persisting disputes about human rights, economics, online security and clashes over sovereignty in the South China Sea.

"Unfortunately, today we only have confrontation," he said.

"We need to re-establish a functional relationship between the two powers."

He called this "essential to address the problems of vaccination, the problems of climate change and many other global challenges that cannot be solved without constructive relations within the international community and mainly among the superpowers".

Two years ago, Guterres warned global leaders of the risk a split in international relations, with the United States and China creating rival internets, currency, trade, financial rules "and their own zero-sum geopolitical and military strategies".

He has now reiterated that warning, adding that two rival geopolitical and military strategies would pose "dangers" and divide the world.

Thus, he said, the foundering relationship must be repaired - and soon.

"We need to avoid at all cost a Cold War that would be different from the past one, and probably more dangerous and more difficult to manage," Guterres said.

The so-called Cold War between the Soviet Union and its east bloc allies and the US and its western allies began immediately after the Second World War and ended with the break-up of the Soviet Union in 1991.

It was a clash of two nuclear-armed superpowers with rival ideologies - communism and authoritarianism on one side, capitalism and democracy on the other.

The UN chief said a new Cold War could be more perilous, because the Soviet-US antipathy created clear rules, and both sides were conscious of the risk of nuclear destruction.

That produced back channels and forums "to guarantee that things would not get out of control", he said.

"Now, today, everything is more fluid, and even the experience that existed in the past to manage crisis is no longer there," Guterres said.

He also said the US-UK deal to give Australia nuclear-powered submarines so it could operate undetected in Asia "is just one small piece of a more complex puzzle ... this completely dysfunctional relationship between China and the United States".

The secretly negotiated deal angered China and France, which had signed a contract with Australia worth at least $A90 billion for a dozen French conventional diesel-electric submarines.

Australian Associated Press