BEIJING-- China's top quality watchdog said Wednesday that more than 10 percent of the nation's electric cables were substandard in its sample checks on three major kinds of products.

The qualification ratio reached only 88.4 percent, the General Administration of Quality Supervision, Inspection and Quarantine said in an online statement on its website.

The quality issues mainly focus on insulating property, measurement, and conductor's electric resistance, the statement said.

The checks found that the problems were a result of the use of inferior production materials and poor manufacturing. As well, some companies were illegally making unqualified products, which have now flooded the rural markets and the nation's affordable housing projects, the statement said.

The administration has shut down 79 companies for illegal operations and ordered more than 400 other companies to correct their production.

The statement also said that local quality regulators have stepped up inspections on the quality of electric cable exports, especially those to the African market.