BEIJING -- China's customs authority seized 137,000 tonnes of illegal trash imports Tuesday in what it called the largest campaign against trash smuggling in recent years.

The smuggled trash included scrap metal and waste mineral residue, the General Administration of Customs (GAC) said in a statement, adding that it also found evidence of 606,500 tonnes of illegal solid waste imports, including scrap plastic.

Nearly 1,300 customs officers in 17 provincial regions, including Guangdong and Tianjin, detained 137 suspects and broke up 39 smuggling rings during the joint action.

It was the third crackdown on trash smuggling launched by the GAC this year. So far, 249 suspects from 81 smuggling rings have been detained, with 217,000 tonnes of waste seized.

China began importing solid waste as a source of raw materials in the 1980s, and has for years been the world's largest importer, despite its weak capacity in garbage disposal. Some companies illegally bring foreign garbage into the country for profit, posing a threat to the environment and public health.

Given rising public awareness and a green development drive, the government decided last year to phase out and completely halt such imports by end of 2019, except for those containing resources that are not substitutable.