China reports most virus cases since pandemic start

China reported more than 20,000 Covid-19 cases on Wednesday, the highest daily tally given since the start of the pandemic as millions in locked-down Shanghai began a new round of testing.

The country's "zero-Covid" strategy has come under immense strain as cases spike, with around 25 million residents of Shanghai -- China's largest city and economic engine room -- ordered to stay at home as the authorities struggle to contain the outbreak.

Until March, China had kept daily cases low with snap localised lockdowns, mass testing, and strict restrictions on international travel.

But the caseload has hit thousands per day in recent weeks, with Shanghai driving the surge of the highly transmissible Omicron variant.