Galapagos Islands: World-famous rock formation Darwin's Arch collapses

A boat full of tourists in the Galápagos Islands have had unexpected front-row seats to a "once in a lifetime event" as a famous rock formation collapsed.

Divers on board the Galapagos Aggressor III watched Darwin's Arch fall into the sea, leaving behind two rocky pillars.

In a post on social media, Aggressor Adventures said the collapse happened "in front of their eyes".

"There are now only two pillars remaining. Some in the dive & travel industry are already referring to this now as 'The Pillars of Evolution'. We will miss this iconic site.

Ecuador's environment ministry confirmed the collapse in a Facebook post.

"This event is a consequence of natural erosion. Darwin's Arch is made of natural stone that at one time would have been part of Darwin Island, which is not open to visits by land.

"This site is considered one of the best places on the planet to dive and observe schools of sharks and other species."

The rock formation, named after the British scientist and explorer Charles Darwin who visited the islands in 1835, is 1000km off South America.

The loss of the rock formation is "a reminder of how fragile our world is", says Jen Jones of charity Galápagos Conservation Trust.

"It really was an icon of the Galápagos landscape and a marker for one of the most awe-inspiring wildlife experiences on Earth, as beneath the waves can be found one of the largest aggregations of sharks in the world," she told The Guardian.