SHANGHAI - Customs in eastern China's Shanghai ordered the return of 7,056 tonnes of suspected smuggled solid waste to where they originated in May.

Most of the waste was undeclared and overdue waste, said the city's customs Monday.

For example, 103 tonnes of old cardboard from Australia that was sent back in five containers in May had been piled high in a Shanghai port for seven years.

The undeclared waste has been a real headache for Shanghai for a long time, said an official with the Shanghai customs. "The city will intensify the inspection on imported waste in the future."

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

Given rising public awareness of environmental protection and China's green development drive, the country decided to phase out and halt such imports by the end of 2019, except for those containing resources that are not substitutable.