People queue to be tested for Covid-19 coronavirus at a nucleic acid collection station in Beijing on October 26, 2021. AFP
Beijing imposed strict border controls after the virus was first detected in China in late 2019, slowing the number of cases to a trickle and allowing the economy to bounce back.
But it has stamped down hard on any local outbreaks and Tuesday's fresh restrictions came as China reported 29 new domestic infections -- including six cases in Lanzhou, the provincial capital of northwestern province Gansu.
Residents of Lanzhou will be required to stay at home, authorities said in a statement.
Officials added the "entry and exit of residents" would be strictly controlled and limited to essential supplies or medical treatment.
China's latest outbreak has been linked to the contagious Delta variant, with the tally from the latest spread hitting 198 cases since October 17.
Health officials have warned that more infections may emerge as testing is ramped up in the coming days to fight the outbreak, which has been linked to a group of domestic tourists.
Strict stay-at-home orders have already been imposed on tens of thousands of people in northern China.
In Beijing -- which reported three new cases Tuesday -- access to tourist sites has been limited and residents advised not to leave the city unless necessary.
Several housing compounds in the capital have also been locked down, and organisers on Sunday indefinitely postponed a marathon at which 30,000 runners were expected.
While the country's case numbers are extremely low compared with elsewhere in the world, China has pursued a zero-case strategy throughout the pandemic.
Authorities are also determined to stamp out the latest outbreak with the Winter Olympics just over 100 days away.
On Tuesday, the official Xinhua news agency reported that the party secretary of Ejin Banner in the northern Inner Mongolia region had been removed from his position, "due to poor performance and implementation in epidemic prevention and control".
The city has also been hit by the latest wave which has mostly spread in northern areas in China.
Mass testing is underway in 11 provinces where authorities have suspended inter-provincial tour groups in five areas where cases have been detected, including Beijing.
In a sign of how seriously Beijing is taking the outbreak, the city's police have launched three criminal investigations into alleged Covid safety breaches, deputy director of the city's public security bureau said Sunday.
Earlier, Lanzhou city and parts of Inner Mongolia had already suspended bus and taxi services.