A powerful cyclone that smashed into northeastern Australia could have caused further damage to the under-pressure Great Barrier Reef, turning parts into an "underwater wasteland", scientists warned on Thursday.

There are already fears for the survival of corals in the central and northern areas of the World Heritage-listed marine ecosystem that stretches 2,300 kilometers off the Queensland coast, after two consecutive years of mass bleaching from warming sea temperatures.

While storms can bring relief through rain and cloud cover to corals suffering from heat stress, Tropical Cyclone Debbie, which barreled through the region this week, mostly struck the reef's southern parts, which have not been as seriously impacted by bleaching.

The reef is already under threat from farming runoff, development and the crown-of-thorns starfish, as well as bleaching, which has been blamed on global warming.

Ongoing inclement conditions mean the extent of the damage from Debbie is not yet known.