China's coronavirus cases have hit a seven-month high after a cluster at a test site has driven up numbers as the Delta variant challenges Beijing's grip on the pandemic, reports AFP.

Chinese health authorities have reported 143 new coronavirus infections — 108 of them locally transmitted.

State media has described the current outbreak — which has sparked local lockdowns, mass testing and travel restrictions — as the most severe since the virus emerged in the central city of Wuhan.

In a sign of the anxiety over even relatively minor outbreaks, several officials have been issued warnings for mishandling mass testing, which city authorities said allowed the virus to spread.