China's proposals to impose tougher rules over its vaccine market will help stamp out illegal behavior and strengthen oversight, but will be "complex" to implement, the World Health Organization (WHO) said in a statement on Friday.

The State Council, China's cabinet, said on Wednesday it would tighten supervision of vaccine distribution, with better record keeping for the production, storing and transport of vaccines and tougher punishments for lawbreakers.

The move comes in the wake of a case involving millions of illegal trades of vaccines through a black market drugs ring, which ignited public ire and underscored regulatory weaknesses in the world's second largest pharmaceuticals market.

The vaccines, including ones against meningitis, rabies and other illnesses, are suspected of being sold in dozens of provinces around China since 2011. They were all "category 2" vaccines, meaning they were sold on the private market.

The new regulations will see these vaccines come under a more tightly-controlled government distribution system, which is used for vaccines within the national immunization program.

WHO China representative Bernhard Schwartl'nder said the changes would "not only ensure illegal activities such as those exposed in Shandong cannot happen elsewhere, but will make the system stronger overall". An illegal vaccine ring had been centered in Shandong province.

"The challenge from here will be in implementation: the proposed changes are powerful and wide-reaching, and some will be complex to put into practice," he added.

The proposals would also improve China's vaccine tracking system, remove incentives for local clinics to make extra money by re-selling unused vaccines and consider how to gradually move more vaccines into the state immunization list.

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China's relatively swift move reflects a wider drive to improve the quality of locally-made drugs and rid the sector of a reputation for corruption, poor quality and fakes.

The case, which has stirred angry debate in China, has so far seen 202 people detained, with 357 officials receiving administrative punishments.