China said Friday that it has effectively locked down Changchun, which has a population of around nine million, as the number of people newly infected with the novel coronavirus has been increasing in the northeastern city.

The municipal government also said it has begun to carry out PCR tests on all citizens in the city, as the ruling Communist Party has pledged to continue implementing its radical "zero COVID" policy.

Residents in Changchun are required to take PCR tests three times, with one family member allowed to go out to buy food and other daily necessities every two days. Corporate activities there have been suspended in principle.

In Changchun, more than 70 people, including those who have no symptoms, have been confirmed to be infected with the virus since early this month, according to health authorities.