BEIJING: China placed a city of four million people under lockdown on Tuesday, ordering them not to leave home except in emergencies, in a bid to eradicate a Covid cluster of just a few dozen confirmed cases. Beijing imposed strict border controls after the coronavirus was first detected in China in late 2019, slowing the number of cases to a trickle and allowing the economy to bounce back.

But as the rest of the world opens up and tries to find ways to live with the virus, China has maintained a zero-Covid approach that has seen harsh local lockdowns imposed over handfuls of cases.

Tuesday's fresh restrictions came as China reported 29 new domestic infections - including six in Lanzhou, the capital of Gansu province in the country's northwest.

The latest outbreak has been linked to the highly contagious Delta variant, with the tally hitting 198 cases since October 17. Thirty-nine have been in Lanzhou. Residents of the city will now be required to stay at home, authorities said in a statement, with the "entry and exit of residents" strictly controlled and limited to essential supplies or medical treatment.

Bus and taxi services had already been stopped in the city, and state media said Tuesday that Lanzhou station had suspended more than 70 trains, including on key routes to Beijing and Xi'an. A Southern Airlines representative told AFP that all its flights from Beijing's Daxing airport to Lanzhou were cancelled due to public safety, with no resumption date given.

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 who travelled from Shanghai to several other provinces. Strict stay-at-home orders have already been imposed on tens of thousands of people in northern China.