Police in eastern China have detained 37 people implicated in a scandal involving the selling of poorly refrigerated and probably ineffective vaccines, state media reports.
The scandal came to light after police last month announced the detentions of a woman and daughter thought to have sold nearly $US100 million ($A131 million) worth of the suspect products nationwide since 2011.
The scandal re-enforces longstanding concerns among the public over the safety of food and medicine.
Nine pharmaceutical wholesalers believed to have sold the vaccines are being investigated.
Chinese Premier Li Keqiang issued orders late Tuesday for government administrations to work together to conduct a thorough investigation.
Along with prosecuting the criminals involved, government officials found guilty of negligence should be held to account, Li said, according to the official government website.
"This vaccine safety incident has created deep concern among the public and laid bare numerous regulatory loopholes," Li was quoted as saying.
The Food and Drug Administration on Monday ordered a thorough check on where the vaccines were distributed and how they may have been used.
The central government administration demanded local authorities investigate the nine wholesalers believed to have sold the vaccines.
The vaccines included those for hepatitis B, rabies, mumps and Japanese encephalitis.
The China office of the World Health Organisation said it stood ready to provide support to Chinese health authorities.
It said that vaccines need to be stored and managed properly or they can become less effective and that children risked not being protected from the disease against which they were supposed to have been vaccinated.
"It is important to note, however, that improperly stored or expired vaccine seldom if ever causes a toxic reaction - therefore there is likely to be minimal safety risk in this particular situation," the WHO said.
One of the two women initially detained, a 47-year-old doctor with the surname Pang, is alleged to have sold about 2 million doses of suspect vaccines, according to state media reports. Shandong's provincial food and drug safety administration has publicised a list of buyers and sellers.
Police in Shandong province detained a total of 37 suspects implicated in the vaccine scandal, the official Xinhua News Agency reported Wednesday. It gave no details on the suspects, and police who answered calls in Shandong said they had no information on the case.
Amid widespread counterfeiting and lax enforcement, China has struggled to ensure food and drug safety. Past scandals have involved phony infant formula discovered to be nothing but starch and bogus vaccines containing only saline solution.