More than 13 million people in the Chinese city of Xi"an have been ordered to stay at home as authorities attempt to tackle a Covid outbreak there, BBC reported. The northern city has recorded 143 infections since 9 December. Under the new restrictions announced on Wednesday, only one person per household is allowed to leave home every two days to buy essential goods. China has a strict zero-Covid strategy, using mass testing and lockdown to stop outbreaks. The country is on high alert for Covid as it gears up to host the 2022 Winter Olympics in February. Residents of Xi"an, known for its Terracotta Warriors, are not allowed to leave the city unless they have extenuating circumstances and approval from officials to so do. The restrictions came into effect at midnight on Thursday local time. It is not yet known how long the restrictions will last. Millions of tests have been conducted in Shaanxi province, where Xi"an is located. Long-distance bus stations have already closed and checkpoints have been installed on motorways into the city. A large number of flights from Xi"an"s airport have been cancelled. Non-essential businesses have closed and local government employees have been told to work from home. Last weekend authorities had already closed indoor facilities such as bars, gyms and cinemas as a precaution, according to state-run Global Times. Officials say the outbreak is the Delta variant of Covid and have not mentioned Omicron. State media have been reporting this week that Xi"an is facing a "dual epidemic" as there have been "several reported cases of haemorrhagic fever, a natural epidemic disease with a high fatality rate". However, this is reported as being a "common" seasonal disease in northern China, and predominantly concentrated in rural areas. China has admitted that Covid-19 remains the "biggest challenge" to the Winter Olympics. The country, where the virus was first recorded, has confirmed more than 113,000 cases and 4,849 deaths.