US President Donald Trump has met with Chinese President Xi Jinping in South Korea, shortly after saying he would order the resumption of US nuclear weapons testing.

“We are going to have a very successful meeting, I have no doubt. But he is a very tough negotiator,” Mr Trump said as he shook hands with Mr Xi, who showed little expression.

He said a trade deal with China could be signed on the same day.

As they sat down with their delegations to begin talks, Mr Xi told Mr Trump via a translator it was normal for the two leading economies of the world to have frictions now and then.

“A few days ago … our two economic and trade teams reached basic consensus on addressing our respective major concerns and made encouraging progress … I am ready to continue working with you to build a solid foundation for China-US relations,” Mr Xi added.

Mr Xi also said that China’s development did not contradict Mr Trump’s vision of “Making America Great Again”, China’s state news agency, Xinhua, reported.

A clseoup of a man outside a car

The comments came ahead of a meeting with Xi Jinping. (Reuters: Yonhap)

Ahead of the meeting, Mr Trump ordered the Department of Defense to immediately resume testing nuclear weapons on an “equal basis” with other nuclear powers.

“Because of other countries testing programs, I have instructed the Department of War to start testing our Nuclear Weapons on an equal basis. That process will begin immediately,” Mr Trump said on Truth Social.

“Russia is second, and China is a distant third, but will be even within five years.”

President Vladimir Putin said on Wednesday Russia had successfully tested a Poseidon nuclear-powered super torpedo that military analysts say is capable of devastating coastal regions by triggering vast radioactive ocean swells.

As Mr Trump has toughened both his rhetoric and his stance on Russia, Mr Putin has publicly flexed his nuclear muscles with the test of a new Burevestnik cruise missile on October 21 and nuclear launch drills on October 22.

The United States last tested a nuclear weapon in 1992.

Two men meet in front of flags.

Donald Trump and Xi Jinping ahead of their trade talks. (Reuters: Evelyn Hockstein)

Tests provide evidence of what any new nuclear weapon will do — and whether older weapons still work.

Mr Trump had met with Mr Xi to discuss trade frustrations between the world’s two largest economies.

The meeting in the southern Korean port city of Busan is the first between the leaders since Mr Trump returned to office in January.

A close of up a stern Donald Trump.

Donald Trump looks on as the meeting gets underway. (Reuters: Evelyn Hockstein)

Both countries have become increasingly willing to play hardball over areas of economic and geopolitical competition — which analysts see as a new Cold War.

The trade war reignited this month after Beijing proposed dramatically expanding curbs on exports of rare-earth minerals vital for high-tech applications, a sector China dominates.

Mr Trump vowed to retaliate with additional 100 per cent tariffs on Chinese exports, and with other steps including potential curbs on exports to China made with US software — moves that could have up-ended the global economy.

Reuters