Chinese Premier Li Keqiang has called for an immediate investigation into the sale of 250,000 faulty rabies vaccines as panic grows over product safety.

Outrage swept Chinese social media on Monday as regulators and officials tried to contain fallout over revelations that one of the country's largest vaccine makers had been giving children defective vaccines. On Sunday, Chinese Premier Li Keqiang urged severe punishment for the people involved, saying the incident had "crossed a moral line".

Regulators last week ordered the Jilin-based Changsheng Biotechnology to stop production of a rabies vaccine, after investigators found fabricated production and inspection records during an inspection that was prompted by a tip off, the BBC reported. However, Changsheng said that authorities were punishing the company over a "substandard" DTaP vaccine for diphtheria, pertussis and tetanus.

On Sunday, China's food and drug administration said it was investigating Changsheng and that all production had been halted. The company issued a statement expressing its "deepest apology". There were no reports of injuries or side effects from the vaccines and Chinese officials and state media released statements promising accountability.

"We will resolutely crack down on illegal and criminal acts that endanger the safety of peoples' lives, resolutely punish lawbreakers according to the law, and resolutely and severely criticise dereliction of duty in supervision," Li said in a statement posted on a government website. According to a report by Xinhua news agency, an official said the company had "fabricated production records and product inspection records", as well as "arbitrarily changed process parameters and equipment" during production.

According to state media outlet CGTN, over 250,000 doses of DTaP in the batch had already been sold to disease control and prevention centres in eastern China. The company was ordered to pay a fine of 3.4 million yuan ($510,000). "Thousands of mothers around the country are worried. Over 200,000 children could be affected. What kind of society am I living in?" asked one woman on Weibo.

"My son will be vaccinated next month. I don't know whether or not to let him," said another. Chinese censors also identified the issue as highly sensitive. This is not the first time substandard vaccines have been produced in China. In 2016, an illegal vaccine ring which involved hundreds of people was uncovered.