BEIJING (REUTERS) - China's Qingdao city customs uncovered soybean smuggling worth 5.46 billion yuan (S$1.18 billion) last year, in one of the biggest such cases in the country in years, a state-run newspaper reported.

The official Legal Daily, in a report published on Monday, said a trading company was suspected of smuggling soybeans after customs officials assessed soy prices for potential risk, but it did not name the company involved.

The case came to light after the customs unit in the eastern coastal city seized some 730 contracts, some of which were falsified, and got access to 80,000 emails, the paper said. The unit also arrested four people in the cities of Linyi, Dalian and Shenzhen, it reported.

Customs officials could not be reached for comment.

Qingdao Customs last year said they had detained three employees at a subsidiary of the Japanese trading giant Marubeni Corp on suspicion of smuggling.

It was unclear if the Legal Daily report on the soybean smuggling related to the Marubeni investigation or to a separate case.

China is the world's largest buyer of soybean, importing more than 60 per cent of the estimated global trade of 116 million tonnes in 2014/15, data from the U.S. Department of Agriculture showed.

Beijing launched a special campaign, dubbed as "Green Wind", against smuggling of grains, sugar and cotton last year and uncovered 487 cases of tax evasion valued at 7.1 billion yuan (S$1.54 billion) in the first nine months of 2014, the government said.