A medical worker collects a swab from a resident during a mass testing for the coronavirus disease (Covid-19) at a makeshift testing site at a stadium in Guangzhou, Guangdong province, China May 30, 2021. - cnsphoto via Reuters SHANGHAI, May 31 (Reuters): China on Monday reported a sudden surge in Covid-19 infections in the country's south, with 18 new local cases on May 30 in the city of Guangzhou, causing a flurry of flight cancellation. Of the 27 new coronavirus cases reported by the national health authority in its daily updates, only 7 infections were imported, with the remainder origina...