Washington DC - A sonar image suspected of showing the remains of the plane of Amelia Earhart, the famed American aviatrix who disappeared over the Pacific in 1937, has turned out to be a rock formation.

Deep Sea Vision (DSV), a South Carolina-based firm, released a blurry image in January captured by an unmanned submersible of what it said may be Earhart's plane on the seafloor.

Not so, said the company in an update on Instagram this month.

"After 11 months the waiting has finally ended and unfortunately our target was not Amelia's Electra 10E (just a natural rock formation)," Deep Sea Vision said.

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"As we speak DSV continues to search," it added. "The plot thickens with still no evidence of her disappearance ever found."

The image was taken by DSV during an extensive search in an area of the Pacific to the west of Earhart's planned destination, remote Howland Island.

Earhart went missing while on a pioneering round-the-world flight with navigator Fred Noonan.

Her disappearance is one of the most tantalizing mysteries in aviation lore, fascinating historians for decades and spawning books, movies, and theories galore.

The prevailing belief is that Earhart (39) and Noonan (44) ran out of fuel and ditched their twin-engine Lockheed Electra in the Pacific near Howland Island while on one of the final legs of their epic journey.

Earhart, who won fame in 1932 as the first woman to fly solo across the Atlantic, took off on May 20, 1937 from Oakland, California, hoping to become the first woman to fly around the world.

She and Noonan vanished on July 2, 1937 after taking off from Lae, Papua New Guinea, on a challenging 2,500-mile flight to refuel on Howland Island, a speck of a US territory between Australia and Hawaii.

They never made it.