According to Reuters, buyers have been curbing bookings of the animal feed ingredient in light of African swine fever which has decimated the nation's pig herds.

China bought 6.3 million tonnes of soybeans from Brazil in May, down from 9.124 million tonnes the previous year, data from the General Administration of Customs showed.

That comes as China has reported 137 outbreaks of swine fever in almost all of its provinces and regions since it was first detected in the country in early August 2018.

The decline in soy purchases from Brazil also followed hopes earlier in the year that a trade war between China and the United States would end, with buyers holding off on South American imports in expectation of more US cargoes. However, trade tensions escalated again in early May.

The United States was the second-largest supplier of soybeans to China before the trade war, but imports from the country fell sharply after Beijing slapped tariffs of 25 percent on US cargoes.

"May shipments were mainly booked in April and March, when the market was hopeful that US beans would be able to come into China. So crushers did not stock up on beans," a manager at a major feed producer in northern China said before the customs data was issued.

"Crushers also did not book that many beans due to African swine fever," said the manager, who declined to be identified as he was not authorised to speak to the media.

Swine fever may reduce China's pork output by about 30 percent this year, according to Rabobank.

China's May soybean imports from the US were at 977,024 tonnes, up from 489,539 tonnes in the previous year, the customs data showed.

In total, China brought in 7.36 million tonnes of soybeans in May, customs data showed earlier this month.