China’s Commerce Ministry said on Tuesday that Chinese companies have stopped buying U.S. agricultural products.

The move comes after U.S. President Donald Trump last week signaled he would set new tariffs on US$300bn more of Chinese imports from Sept. 1.

“Related Chinese companies have suspended purchases of U.S. agricultural products,” China’s Ministry of Commerce said in an online statement posted shortly after midnight in Beijing on Tuesday.

China’s state-run Xinhua News Agency called the Trump's proposed tariffs a “serious violation” of an agreement reached in June with Chinese President Xi Jinping.

Agricultural products, especially soybeans, have been at the center of the escalating US-China trade war, with the U.S. insisting that China must make substantial purchases of the crop as part of any trade deal.

American Farm Bureau Federation president Zippy Duvall said in a statement on Monday: “China’s announcement that it will not buy any agricultural products from the United States is a body blow to thousands of farmers and ranchers who are already struggling to get by"

“In the last 18 months alone, farm and ranch families have dealt with plunging commodity prices, awful weather and tariffs higher than we have seen in decades.

“Farm Bureau economists tell us exports to China were down by $1.3 billion during the first half of the year. Now, we stand to lose all of what was a $9.1 billion market in 2018, which was down sharply from the $19.5 billion U.S. farmers exported to China in 2017."

From 2017 to 2018, U.S. agricultural exports to China fell more than 50%, dropping to US$9.1 billion, the Federation said. And from 2000 to 2017, U.S. agricultural exports to China increased by 700%.

Volumes of key U.S. fruit exports to China - including cherries, table grapes, citrus and apples - have already fallen sharply since China first implemented tariffs on a range of U.S. agricultural products last year.