Hong Kong recorded nine new Covid-19 cases on Thursday, with three locally transmitted infections coming from unknown sources.On the eve of a further relaxation of the city’s social-distancing measures, health officials warned the public not to lower their guard amid a recent decline in infections, saying authorities would step up enforcement against those violating the rules still in place.“The reopening of some premises does not mean there is no risk,” said Dr Chui Tak-yi, undersecretary for…