On Sunday, Deputy Prime Minister Truong Hoa Binh, head of the National Steering Committee on the Prevention and Control of Smuggling, Trade Fraud and Counterfeit Goods, directed agriculture, defense, finance and trade authorities to inspect the sales of crawfish in the country, despite it being listed a foreign species banned from being imported since 2013.

Vietnam's 2018 Law on Biodiversity also prohibits all activities related to its breeding and distribution.

Binh said government agencies have to look into all activities related to breeding and trading of the species and punish anyone violating the rules.

Vietnamese scientists have labelled crawfish as a species harmful to agriculture after a pilot breeding program in the northern province of Phu Tho in 2012.

The species reproduce quickly and can withstand environmental changes. With their strong claws, they easily cut paddy stalks, feed on many species of young plants and burrow and destroy embankments, said Bui Quang Te of the Research Institute for Aquaculture.

"If crawfish spread across fields in Vietnam, they could spread diseases and viruses that could damage the crops," he said.

Dang Huy Huynh, former head of the Institute of Ecology and Biological Resources, said "crawfish feed on almost all kinds of aquatic species and compete for food with local species, and if they live together in the same environment, it is possible that some local fish or shrimp species could disappear."

Despite the ban, the import and distribution of crawfish havecontinued unchecked because they have become a favored delicacy among the Vietnamese.

Crawfish used to cost up to VND1 million ($43) per kilogram in restaurants, but thanks to its popularity, prices have dropped to VND250,000-500,000, traders told VnExpress.

China and the U.S. are the two major exporters of the crustacean to Vietnam.

Managing the trade of crawfish from China, however, has been a hard task because usually they are imported in small quantities via border gates.