Citizens of Beijing, spooked by the harsh lockdown imposed on Shanghai, swarmed supermarkets and panic-bought food Monday after authorities said a COVID outbreak in the capital was “spreading stealthily from sources that remained unknown” and was “developing rapidly.” The city reported 19 cases Monday, 14 of which were symptomatic. Beijingers stripped shelves ahead of a feared Shanghai-style lockdown, now in its fourth week, which has been accompanied by food shortages, disrupted services, and growing popular outrage. Beijing is now demanding a negative COVID test to enter the city, and one affluent district, Chayong, has seen more than a dozen residential buildings locked down.