Health officials in northern China are reimposing lockdowns to curb the spread of coronavirus, with health officials warning of a worsening outbreak after the country recorded more than 100 cases in as many as 11 provinces over the last week.

“Since October 17, there have been multiple scattered local outbreaks in China, and they’re expanding rapidly,” Mi Feng, a spokesman at the National Health Commission (NHC), CNN reported.

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“There is an increasing risk that the outbreak will spread even further.”

The rapid spread comes despite about 75% of China’s population — or more than a billion people — being fully vaccinated, according to Mi.

The caseload of China’s latest outbreak pales in comparison with those of some other countries, including Singapore and the United Kingdom. But the scope of its spread has worried the Chinese government.

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It is reportedly said that the outbreak was first detected on October 16 among a tour group of fully vaccinated senior citizens from Shanghai who travelled in several northern regions. Among the 133 infections reported as of Sunday, 106 were linked to 13 tour groups, according to Mi.

Infections have been reported in nearly a third of the country’s provinces and regions, with all medium- and high-risk regions concentrated in Inner Mongolia, Gansu, Ningxia, Guizhou and Beijing. 

Meanwhile, authorities have banned travel agencies from organizing cross-provincial tours in these regions.