The coral is so immense that researchers sailing the crystal waters of the Solomon archipelago initially thought they had stumbled across a hulking shipwreck. 

"Just when we think there is nothing left to discover on planet earth, we find a massive coral made of nearly one billion little polyps, pulsing with life and colour," marine ecologist Enric Sala said. 

The standalone structure had been growing for some 300 years, the researchers said, formed from a "complex network" of tiny coral polyps.  It was distinct from a coral reef, which is made from many distinct coral colonies, they explained.

Measuring 34 metres wide (111 feet) and 32 metres long (104 feet), the team said the "mega coral" was three times bigger than the previous record holder -- a coral dubbed "Big Momma" in American Samoa. 

"While Big Momma looked like a huge scoop of ice cream plopped down on the reef, this newly discovered coral is as if the ice cream started to melt, spreading forever along the seafloor," said lead scientist Molly Timmers. 

It was longer than a blue whale and was thought to be "so colossal" that it could "be seen from space". 

The coral was discovered at the southeastern tip of the Solomon Islands in an area known as the Three Sisters.  It was spotted by a National Geographic team embarking on a scientific expedition in the region.