BEIJING — China’s imports of solid waste continued to decline in the first five months of the year as the country tightened enforcement of a ban on solid waste imports.

Imports of plastic, paper and metal waste totaled 5.9 million tons during the January-May period, down 30.2 percent from the same period last year, according to the General Administration of Customs.

In May alone, solid waste imports reached 1.17 million tons, down from 1.3 million tons in April.

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

As part of its anti-pollution efforts, the government decided to phase out and halt such imports by the end of 2019, except for those containing resources that are not substitutable.

While banning imports of 24 types of solid waste, including plastics and paper, the government is also working on improving the domestic solid waste recycle rate. The amount of domestic recycled solid waste is expected to increase from 246 million tons in 2015 to 350 million tons by 2020.