At least 10 prefecture-level areas in North China's Inner Mongolia autonomous region have been hit by a new round of COVID-19, with some places imposing rigid control measures to curb its spread.

The region reported 13 locally transmitted confirmed COVID-19 cases and 661 asymptomatic carriers on Thursday, further aggravating the region's epidemic situation, according to the region's Health Commission.

As of Thursday, Inner Mongolia had reported 381 local confirmed cases and 1,554 asymptomatic carriers since the outbreak first emerged on Sept 28 in Hohhot.

Most of the cases are in Hohhot city, the commission said.

"The current outbreak in Hohhot involved the Omicron subvariant BF.7, which is more infectious and transmissible, so it's easy to bring on large-scale transmission," Xiao Fang, vice-mayor of Hohhot, said at a news conference on Friday. "At present, the city is facing a severe and complex epidemic situation, with rapid caseload growth and sporadic cases in multiple places."

More medical personnel and facilities have been allocated to ensure treatment and quarantine. The city has increased the number of designated hospitals and started using makeshift hospitals, Xiao added.

This is the first outbreak on the mainland involving the subvariant. Cases with the strain have also risen in Europe and the United States. The new BF.7 strain, also known as BA.5.2.1.7, is reportedly more contagious and immune evasive.

The city will strengthen its management at the community level starting on Saturday, the first workday after the seven-day National Day holiday, Zhao Zhong, deputy head of the city's commission for political and legal affairs, said at the news conference.

Residents are required to work from home. Primary and secondary schools, as well as kindergartens, will delay the resumption of on-site classes, Zhao said.

According to Xiao, the city has designated 357 areas as high-risk and three as medium-risk.

With sporadic cases, some urban areas and counties in Ulaanhot and Hulunbuir started temporary static management on Friday and carried out mass nucleic acid testing.