CAPE YORK (Australia) • Scientists have discovered a massive coral reef - higher than the Empire State Building - at the northern tip of the Great Barrier Reef.

Measuring about 500m high, the detached reef is the first to be discovered in more than 120 years, California-based non-profit group Schmidt Ocean Institute announced earlier this week.

This means the reef is also taller than the 305m-tall Sydney Tower and the 452m-high Petronas Twin Towers. The Empire State Building is 381m in height.

"This unexpected discovery affirms that we continue to find unknown structures and new species in our ocean," said Ms Wendy Schmidt, co-founder of the Schmidt Ocean Institute.

The reef was first discovered on Oct 20 by Australian scientists aboard the institute's research vessel Falkor while doing underwater mapping of the northern Great Barrier Reef seafloor. The scientists are on a 12-month exploration of the ocean surrounding Australia.

The team used an underwater robot, SuBastian, to explore the new reef.

James Cook University's Dr Robin Beaman, who was leading the team of scientists who discovered the reef, said they were surprised and elated by what they found.

"To not only 3D-map the reef in detail, but also visually see this discovery with SuBastian is incredible," said Dr Beaman.

According to the institute, the base of the blade-like reef is 1.5km wide. It then rises 500m to its shallowest depth of only 40m below the sea surface.

Dr Jyotika Virmani, executive director of the institute, said: "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."

This newly discovered detached reef adds to the seven other tall detached reefs in the area that have been mapped since the late 1800s. They include the reef at Raine Island, the world's most important green sea turtle nesting area.

The Great Barrier Reef runs 2,300km down Australia's north-east coast spanning an area half the size of Texas.