The number of daily new cases of Covid-19 is surging in China, in the worst wave of infections since the pandemic began more than two years ago, news agency MIA informs.

China’s health commission reported a daily record of more than 3,100 new cases across 19 regions on Sunday. In response, Beijing is introducing mass testing, curfews and restrictions on transport and is closing schools and universities.

The authorities have also started building temporary hospitals with thousands of beds in several cities in order to isolate those who are infected.

There were only a few dozen infections per day just weeks ago. Shanghai’s population of 26 million, and the 9 million living in Qingdao, have been told not to leave those cities if possible.

Those who cannot delay travel have to show a negative test taken within the past 48 hours, as must anyone landing in China.

Officials imposed a lockdown on Changchun, population 9 million, on Friday, with one person per household permitted to go shopping every two days. Further south, restrictions were also introduced in the megacities of Dongguan and Shenzhen.

The highly-transmissible Omicron strain presents a major challenge to China’s strict zero-Covid strategy. Beijing introduced stringent measures to contain the pandemic in spring 2020, sealing the country off entirely. Under the current rules, anyone who comes to China has to spend three weeks in quarantine. China’s regulations enabled daily life and the economy to largely return to normal, with only limited outbreaks, most of which were successfully contained thanks to curfews, mass testing and quarantine.

The cases reported on Sunday included 1,315 which were asymptomatic, typical of the Omicron strain where cases are often mild, according to scientists.