US President Donald Trump has urged China to quadruple its soybean purchases ahead of a key tariff truce deadline.

In a late-night post on Truth Social, Trump said on Sunday China was worried about a shortage of soybeans and that he hoped it would quickly quadruple its soybean orders from the United States.

China, the world's largest soybean buyer, imported roughly 105 million tonnes last year, just under a quarter coming from the United States and most of the remainder from Brazil. Quadrupling shipments would require China to import the bulk of its soybeans from the United States.

A tariff truce between Beijing and Washington is set to expire on August 12, but the Trump administration has hinted that the deadline may be extended.

It is unclear if securing China's agreement to buy more US soybeans is a condition for extending the truce as Trump looks to reduce China's trade surplus with the United States.

The US soybean industry has been seeking alternative buyers, but no other country matches China's scale. (Reuters)