Hong Kong confirmed nine new Covid-19 cases on Monday, the day before the start of mass testing to identify invisible coronavirus carriers in the city, but arguments continued over the effectiveness and safety of the scheme.More than 553,000 residents had signed up for the programme as of 6pm, while Hong Kong’s leader, her top ministers and bureau chiefs will take the lead and be tested at the government headquarters in Tamar.Chief Executive Carrie Lam Cheng Yuet-ngor’s top advisers will also…