Omicron is not merely a "big flu," but requires a strong immune barrier and medical resources to resist its threats, Shanghai's top coronavirus expert has said.

There is no scientific basis to claim that the Omicron variant of COVID-19 could only lead to severe influenza, said Dr Zhang Wenhong, head of Shanghai's COVID-19 treatment team.

"Without sufficient medical resource, Omicron will bite," Zhang, who is also the director of the National Center for Infectious Diseases, told a local forum on Saturday.