Apparently it has been caused by gale force winds in central Australia kicking up tonnes of red dust from the deserts, which was then carried in by westerly winds.
The last few weeks have been blue skies and hot sunshine so it was strange to look out of the window this morning and see this. It was only watching the news later on in the day that I discovered what was causing it. Just looking out the window the fine dust wasn't clearly discernible, only its effects, so I never thought to close the windows and doors which have been pretty much left open permanently lately due to the hot weather. Which means that we've now got some serious dusting to do indoors!
The dust storm has caused havoc in Sydney, Brisbane and much of the rest of New South Wales and Queensland. You can read more here..