Four new Covid-19 cases have been identified in Melbourne s northern suburbs
NSW health authorities said the new infections serve as a warning to residents
Health boss Brett Sutton said transmission will increase in the colder months
On Tuesday, South Australia announced it will close borders with Victoria
Cases are all close family contacts of each other, living in two separate houses
Victorian Department of Health has extended list of potential exposure sites
Melbourne s list of Covid-exposed venues grows as a Woolworths, food court and Nando s are added dailymail.co.uk - get the latest breaking news, showbiz & celebrity photos, sport news & rumours, viral videos and top stories from dailymail.co.uk Daily Mail and Mail on Sunday newspapers.