US President Donald Trump says he has ordered the resumption of nuclear weapons testing to keep up with rival nations that are ramping up their arsenal stockpiles.

Trump made the announcement in a social media post ahead of his highly anticipated meeting with China’s President Xi Jinping on Thursday (AEDT).

He said that because of testing programs in other countries, he had instructed the US Department of War (his renamed Department of Defence) to “start testing our Nuclear Weapons on an equal basis”.

“That process will begin immediately. Thank you for your attention to this matter!” he wrote on Truth Social.

Trump boasted the US had “more Nuclear Weapons than any other country”.

“This was accomplished, including a complete update and renovation of existing weapons, during my First Term in office,” he wrote.

“Russia is second, and China is a distant third, but will be even within 5 years.”

At Thursday’s meeting with Xi soon after, Trump declined to respond to a question about the post.

He met China’s leader at a South Korean air base for discussions on a possible trade-war truce between the world’s two largest economies.

The meeting in the southern port city of Busan, the first between the leaders since Trump returned to office in January, capped off the his whirlwind trip around Asia.

“We are going to have a very successful meeting, I have no doubt. But he is a very tough negotiator,” Trump said as he shook hands with Xi, adding that the pair might sign a trade deal on Thursday.

As they sat down with their delegations to begin talks, Xi told 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,” Xi said.

Trump has repeatedly expressed optimism about reaching agreement with Xi during the talks, taking place on the sidelines of the Asia-Pacific Economic Cooperation (APEC) summit, buoyed by a breakthrough in trade talks with South Korea on Wednesday.

But with both countries increasingly willing to play hardball over areas of economic and geopolitical competition – which analysts see as a new Cold War – questions remain about how long any trade detente may last.

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.

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 upended the global economy.

“THE G2 WILL BE CONVENING SHORTLY,” Trump posted on Truth Social shortly before landing in Busan.

After a weekend scramble between top trade negotiators, US Treasury Secretary Scott Bessent said he expected Beijing to delay the rare earth controls for a year and revive purchases of US soybeans critical to American farmers, as part of a “substantial framework” to be agreed by the leaders.

Ahead of the summit, China bought its first cargoes of US soybeans in several months, Reuters reported exclusively on Wednesday.

The White House has signalled it hopes the summit will be the first of several between Trump and Xi in the coming year, including possible leader visits to each country, indicating a protracted negotiation process.

But Trump wants some quick progress, in talks being closely watched by businesses worldwide.

Regional strategic tensions, particularly over Beijing-claimed Taiwan, a US partner and hi-tech powerhouse, are an ominous backdrop to the summit.

On Sunday, Chinese state media said Chinese H-6K bombers recently flew near Taiwan to practise “confrontation drills”.

US Secretary of State Marco Rubio said Taiwan should not be concerned about the US-China talks, despite some experts expressing fears that Trump might offer concessions over the island. Washington is required under US law to provide Taiwan with the means to defend itself.

-with AAP