Officials in the northwestern Chinese city of Xi'an have reimposed a lockdown to restrict the movement of 13 million citizens after dozens of COVID-19 cases were reported this month.

Authorities in Xi'an, Shaanxi Province, say they confirmed 43 new cases of coronavirus in the city-- mainly the highly contagious Omicron variant -- between April 2 and 15.

They say the four-day lockdown will last until Tuesday and, while citizens are urged to stay home, supermarkets and medical facilities are allowed to stay open.

Xi'an authorities imposed a strict lockdown after the Delta variant spread in the city between December last year and January this year.

The Chinese government led by President Xi Jinping maintains a zero-COVID policy, and a strict lockdown continues in the country's commercial hub of Shanghai.