Recent video reveals that 95 per cent of Australia's Great Barrier Reef's northern section shows coral bleaching, the ARC Centre of Excellence for Coral Reef Studies says.
The group, from Townsville's James Cook University, filmed over 500 coral reefs over a period of six days from Cairns to Papua New Guinea and says that the most untouched part of the Great Barrier Reef is seeing the most severe bleaching in history.
The World Wildlife Fund released a dramatic video and photos of bleaching on Lizard Island, a different part of the reef, earlier this month.
Corals, which are animals, have a symbiotic relationship with algae that give them their colour and help provide them with food. During stressful conditions such as heat waves, the algae disappear from the corals, leading to coral bleaching. If the stressful conditions last more than eight weeks, the corals can die of starvation.
Authorities this month also said that areas of the World Heritage Site were experiencing the worst bleaching in 15 years, at least partially as a result of the current El Nino weather effect, one of the strongest in two decades.
Scientists said the Great Barrier Reef needs a break in El Nino conditions within weeks if some coral areas are to survive, but the Australian Bureau of Meteorology's most recent forecast says there will be a continuation of El Nino conditions.
2015 was the hottest year on record and 2016 could be even hotter due to El Nino, the World Meteorological Organization has said.
The Great Barrier Reef stretches 2,000 kilometres (1,200 miles) along Australia's northeast coast and is the world's largest living ecosystem. It brings in billions of dollars a year in tourism revenue.
UNESCO's World Heritage Committee last May stopped short of placing the Great Barrier Reef on an "in danger" list, but the ruling raised long-term concerns about its future.