Experts conducted the first flyover of 2017 this week and noticed severe bleaching in the areas of Ingham to the northern extent of the survey near Cairns, the Great Barrier Reef Marine Park Authority said in a news release.
The Great Barrier Reef 's health is in "uncharted territory" after researchers found the natural wonder has endured mass coral bleaching two summers in a row. If the coral dies, it will turn a nasty greenish-brown as other opportunistic algae grow on its surface.
Numerous big tourist sites were spared the worst of the bleaching or recovered quickly, but this year the heat stress is closer to Cairns and other popular sites, as Fairfax Media reported earlier this month.
The agency said more bleaching was being observed in the central part of the reef, which previous year escaped widespread severe bleaching.
The Australian Institute of Marine Science's Dr Neal Cantin said the bleaching was the result of water temperatures increasing by just one degree during a "typical summer".
The images were taken by marine biologist and conservation photographer Brett Monroe Garner, who documented the latest round of coral bleaching in conjunction with Greenpeace.
Bleaching occurs when warm waters prompt coral to expel algae living within their tissues, turning white. the Guardian daily reported.
"There's enough bleaching there to tell us that it is a significant heat-stress event", Russell Reichelt, the authority's chairman, said on Saturday.
While bleaching occurs naturally, scientists are concerned that rising sea temperatures caused by global warming magnifies the damage, leaving sensitive underwater ecosystems unable to recover.
The GBRMPA will send scientists and experts to survey the remaining length of the reef later this month.
"We've started to see the first mortality", Mr Fitzpatrick said.
The coral may die in the six to 12 months after bleaching, meaning the level of mortality on the reef will not be determined until later in the year.
"The 2017 bleaching is still building as we approach the summer peak temperature", Professor Hughes said.
"It's alarming that the reef is bleaching so soon again, giving no time for recovery from the huge losses of corals in the northern third of the Reef in 2016", he said. The situation is still evolving but coral mortality could potentially be even higher than previous year. "In many areas, people are causing declines in coral reefs because of pollution, overfishing, and habitat destruction", he said. "There is no hint from the federal government that they are responding to this as a national emergency".