Australian scientists say warming oceans this year have caused the biggest die-off of corals ever recorded on Australia's Great Barrier Reef.

The Australian Research Council Centre of Excellence for Coral Reef Studies said Tuesday that the worst-affected area was a 700-kilometer (400-mile) swath in the north of the World Heritage-listed 2,300-kilometer (1,400-mile) chain of reefs off Australia's northeast coast.

It found that the northern swath had lost an average of 67 percent of its shallow-water corals in the past nine months.

The center based its findings on dive surveys in October and November.

The governments of Australia and the state of Queensland will update the UNESCO World Heritage Center this week on progress being made to protect and improve the reef, including their response to coral bleaching.