SHENZHEN -?Customs in the southern metropolis of Shenzhen has busted a huge smuggling case, with 57 suspects detained, authorities said Thursday.

Customs staff have confiscated smuggled amber, lithium batteries, medicine, milk powder and other daily articles, in a case worth 227 million yuan (33 million U.S. dollars) in a recent raid, according to Shenzhen Customs in Guangdong Province.H Authorities found more than six tonnes of amber raw materials worth about 70 million yuan, as well as 620,000 lithium batteries in the raid.

"The suspects imported the amber resources from foreign countries and transported them to Hong Kong, before smuggling them to the Chinese mainland," according to an unidentified customs officer. "The buyers then sold the raw materials or processed ones in cities such as Shenzhen and Beijing."

Shenzhen customs have launched four crackdowns on smuggling so far this year, with 31 smuggling gangs busted and 113 suspects detained.