More than 17,700 people had been swabbed by Monday morning at part of a drive to test airport cargo staff
Hundreds of flights at one of China's busiest airports were cancelled Tuesday as Shanghai raced to bring a local coronavirus outbreak under control.
Health officials have tested thousands of staff at Pudong International Airport since a small cluster of Covid-19 cases in the city was linked to several cargo handlers.
China -- where the virus first emerged late last year -- has largely brought the pandemic under control through travel restrictions and lockdowns, but it is now battling a number of domestic outbreaks in different cities.
Shanghai has reported seven local infections linked to the airport this month, with most cases found in the past few days.
The outbreak has sparked plans to give high-risk workers at the travel hub an experimental vaccine China has already been providing to state employees, international students and essential workers heading abroad since July.
On Tuesday, figures from data services firm VariFlight showed that over 500 flights out of Pudong Airport had been called off -- nearly half the day's scheduled flights.
Almost half of scheduled inbound flights were also cancelled.
More than 17,700 people had been swabbed by Monday morning at part of a drive to test airport cargo staff, state news agency Xinhua reported, with those infected including employees at logistics firms FedEx and UPS.
Videos shared Sunday night on social media appeared to show a large crowd at the airport trying to push their way into a multi storey car park where the testing was taking place and being held back by a row of people wearing full hazmat suits.
Later footage published by Shanghai health officials showed rows of people queuing at what appears to be the same location and being ushered to testing stations by health workers.
Nearly half of all scheduled flights were also cancelled at Tianjin International Airport, a northern port city testing around 2.6 million people to try and bring a local cluster under control.
Tianjin reported five local cases on Saturday and another on Tuesday.
China has been rolling out mass-screening campaigns in response to the emergence of local Covid-19 cases, in some instances collecting test samples from entire districts or cities.
Authorities have in recent days shifted their focus to imported frozen food and other inbound shipments, which have been blamed for a resurgence of local infections.