Scientists have discovered an enormous coral reef at the northern tip of Australia's Great Barrier Reef, the first such discovery in 120 years.
At 500m (1,640ft) high, the reef is taller than New York's Empire State Building and the Petronas Twin Towers in Kuala Lumpur, Malaysia, reports the BBC.
Scientists on a 12-month mission found the structure, detached from the Great Barrier Reef off Cape York, last week. They were conducting 3D mapping of the sea floor in the area.
A team aboard a research vessel owned by the Schmidt Ocean Institute (SOI), a non-profit group based in California, used an underwater robot to explore the reef. Known as SuBastian, the robot live-streamed video of the discovery on Sunday and posted it to YouTube.
"To find a new half-a-kilometre tall reef in the offshore Cape York area of the well-recognised Great Barrier Reef shows how mysterious the world is just beyond our coastline," said SOI executive director Dr Jyotika Virmani.
"This powerful combination of mapping data and underwater imagery will be used to understand this new reef and its role within the incredible Great Barrier Reef World Heritage Area."
The Great Barrier Reef, the world's largest coral reef, is home to more than 1,500 species of fish, 411 species of hard corals and dozens of other species.
Stretching over 2,300km (1,400 miles), the reef was designated a World Heritage site in 1981 for its "enormous scientific and intrinsic importance".
In recent years, it has been vastly damaged by warmer seas which have killed off coral, dispersed other marine life and sped up growth of algae and other contaminants.
A study published earlier this month found the Great Barrier Reef had lost more than half of its corals since 1995 due to warmer seas driven by climate change.