Closing state borders

is not something done lightly.  Efforts to keep the  Covid19 virus contained have necessitated that.
The disruption to the lives of so many people will have an enormous social and economic impact - and not just on those living in the region "locked down". People cross state borders every day. Some live in one state and work in another. They go shopping for essential items across the border and much more. Understandably there have been many questions and, from some, complaints.
There was also an entirely unwarranted criticism from a columnist about some remarks which were made. The columnist in question would be aware of sec.92 of Downunder's constitution. It reads:

  On the imposition of uniform duties of customs, trade, commerce, and intercourse among the States, whether by means of internal carriage or ocean navigation, shall be absolutely free. But notwithstanding anything in this Constitution, goods imported before the imposition of uniform duties of customs into any State, or into any Colony which, whilst the goods remain therein, becomes a State, shall, on thence passing into another State within two years after the imposition of such duties, be liable to any duty chargeable on the importation of such goods into the Commonwealth, less any duty paid in respect of the goods on their importation.

<sup>It is the word "intercourse" which is causing the difficulties here
 
"intercourse" is the ability "to pass to and fro among the States without burden, hindrance or restriction". (Cole v Whitfield)

Despite the wording in the Constitution however decisions of the High Court have allowed some restrictions to occur. 
Whether state Premiers have the power to close state borders and under what circumstances is something sec, 92 does not state.  If the current closure of state borders is challenged in the courts then it is highly likely that the High Court will take the "individual rights" approach - and say that the closure was a "permissible burden or reasonable regulation". 
What powers state Premiers have within their own states to order a lock down will vary with the different state constitutions. If they are questioned then the courts are going to have to find a way through to the greatest public good. 
I don't envy them. 
Criticising the present Prime Minister for acknowledging the constitutional issues involved is hardly helpful.</sup>