Chinese customs has confirmed that a nationwide crackdown on smuggling of agricultural products will include all major crops that the country produces, the official Xinhua news agency reported late Wednesday.

China's agricultural commodities are often priced significantly higher than many international markets as a result of generous government support schemes for farmers and inefficient local production.

The price gaps have spurred a burgeoning trade in unofficial imports across China's southern border, hurting domestic markets.

The year-long campaign kicked off earlier this year and will focus on grain, sugar, cotton, edible oil and frozen foods, customs spokesman Zhang Guangzhi told Xinhua. Frozen foods typically include beef and seafood.

Although customs officials had earlier said that an anti-smuggling campaign was taking place this year, exactly which commodities were included had not been confirmed.

Customs will cooperate with the Ministry of Agriculture, chief planning agency the National Development and Reform Commission, the Ministry of Commerce and the quarantine bureau to target each phase of the smuggling chain, Xinhua said.

But industry insiders have been sceptical about the impact of such crackdowns, saying that the grey market trade in such goods would continue as long as a price differences remained.

The volume of smuggled sugar was as much as 1 million tonnes in 2013, Ge Junjie, vice president of Shanghai food conglomerate Bright Foods, told parliamentary delegates earlier this month citing industry estimates. Legal imports stood at around 4.5 million tonnes.

Customs investigated 2,275 cases of suspected smuggling in the first two months of this year, worth 4.1 billion yuan ($660 million), according to the Xinhua report.