The closing of our border is a decision that should not be taken lightly. I am sure the PM is receiving a lot of briefings from various sector experts. The PM will have at hand far more information at hand than that which is available here. Closing the border may well be the wrong option and may hinder our ability to combat the virus and maintain the treatment of other conditions.
I wonder if it is because a lot of other stuff is also transported on passenger planes, such as medications. So if those planes aren't flying, then it won't get delivered. I would hope there are contingencies in place or maybe that is what they are working on.
I see Australia have now banned gatherings of more than 500 people. Doesn't includes schools or public transport. I would have thought public transport would be a bit of a problem. I remember when I used to catch the train, I used to always get colds, as they were often overloaded.
Australia is a bad example. ScoMo waited till the Formula 1 teams arrived, THEN he banned Italy (who have many F1 people) Then see what happened.