Shanghai police have investigated 310 cases involving 318 individuals of being illegally engaged in courier business without an official pass since the city's coronavirus-induced lockdown in the beginning of April, a senior police officer in the city said on Sunday.

Altogether 103 of them have been put under administrative detention, and suspects in other cases may also face administrative or criminal penalty after further investigations, said Fan Hongfei, chief of the legal corps at Shanghai Public Security Bureau, at a municipal press briefing.

The police will keep up crackdowns of such violations, he said. Individuals working as couriers without a pass will be detained for 10 days and fined 500 yuan ($76).

Anyone who clearly knows that he or she is a close contact of an infection but still works as a courier will be investigated for the crime of obstructing the prevention of infectious disease according to the law.

Anyone who knows that he or she is a confirmed or suspected infection but still engages in courier business will be investigated for the crime of endangering public safety by dangerous methods.

"Couriers are an important team in delivering necessary supplies amid the epidemic, and they have frequent contact with the public. If they've contacted the virus and still go to work, they'll directly endanger the health of the public and affect the overall realization of the dynamic zero COVID," said Fan.

Official data showed that there are more than 87,000 couriers working in the municipality currently. Their electric passes are validated regularly based on their health QR codes and negative nucleic acid test results taken within 48 hours.