The Chinese customs authority said it had seized more than 8,500 tonnes of highly-polluting used tires smuggled from the United States, the biggest amount in recent years.

Smugglers pretended they were importing rubber and shipped the pollutants to the coastal city of South China's Guangzhou via Hong Kong between December 2008 and February 2009, the General Administration of Customs said Thursday.

The Huangpu Customs officials in Guangzhou found in late December 366 uncleared containers of the smuggled waste at the Dongjiangkou Port, which had lain there for almost a year, said Chen Wen, an inspection department official with the customs.

The containers, if lined up, would stretch a length of 4.7 kilometers, according to customs officials.

Transporting each tonne of waste tires from the United States to China cost only four to 10 U.S. dollars, but smugglers could make great profits by using the waste for oil refining and tire retreading, said Cai Hongyu, an official in charge of suppressing smuggling in the Huangpu Customs.

Tires made from the waste materials pose potential safety hazard.

Investigation found the suspects had tried to get the license for rubber imports to cover the smuggling of the waste tires, Cai said.

Three suspects were arrested and admitted their violations, he said.

China bans importing waste tires which threaten environment and health seriously as they will not decompose even if they are buried underground for 100 years.

Exporting waste to developing countries has become a growing business as developed nations seek to reduce the environment cost on their own soil and smugglers eye great profitability from the dealing.

Since 2005, the Chinese customs has nabbed 44,275.8 tonnes of solid waste in 229 cases. More than 600 smugglers have received criminal punishment.