Apple’s business is under threat from a widespread coronavirus outbreak in China, with supply chain experts warning of a growing risk of months-long disruption to the production of iPhones.

The US tech giant has had to contend with more than a month of chaos at its main assembler Foxconn’s megafactory in Zhengzhou, China, known as “iPhone City,” following a Covid-19 outbreak that started in October.

Foxconn has moved some of its production to other factories across China, while Apple has worked with components suppliers to alleviate unusually long wait times—about 23 days for customers buying high-end iPhones in the US, according to research by Swiss bank UBS.