As many Shanghai residents shelter from Covid at home, a common sight on the megacity's suddenly subdued streets is the racing, swerving scooters of food-delivery riders. At a sorting centre in central Shanghai run by Dingdong Maicai, staff are working overtime to handle double the demand of a week ago, when the metropolis of 25 million people began battening down the hatches. "We are an iron army. Whatever artillery fire we face, we react quickly," said Zhang Yangyang, manager of the Dingdong sorting depot. IMAGES AND SOUNDBITES ARRANGED IN SEQUENCES