Australia is being urged to accelerate its efforts in rescuing the Great Barrier Reef amid fears the nation will fail to meet its 2050 target.

The Reef 2050 Plan was released by the Australian and Queensland governments in March 2015 to protect and manage the reef, which is at risk of being placed on UNESCO's "danger list".

In a report released in Paris on Saturday, UNESCO praised progress in the inception and initial implementation of the rescue plan but voiced "serious concern" over the scale of mass bleaching to the reef.

"Progress towards achieving water quality targets has been slow and the most immediate water quality targets ... are not expected to be achieved within the foreseen time frame," the UNESCO report said.