Scientists have been left baffled as to how a dead humpback whale ended up in the Amazon, miles away from its natural habitat.

Scientists rushed to find the carcass, estimated to be 11m long and 6m wide, after videos of a flock of vultures surrounding the decomposing mammal, appeared online.

The whale, believed to be a 12-month-old calf, was found Friday on the island of Marajo in Brazil's north, where the rainforest meets the ocean.

It's understood the whale was 11 metres long and six metres wide. Photo / Instagram
It's understood the whale was 11 metres long and six metres wide. Photo / Instagram

Authorities from the NGO Bicho D'agua said they were stumped as to how the whale ended up so far from its natural habitat in the winter season.

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Remarkable images captured by the marine conservationist group show the dead whale lying in the middle of a swampy mangrove, some 15m from the ocean.

Sampled were taken by biologists before it deteriorated too severely in the hope the tests revealed how the whale ended up there.

The project's president Renata Emin speculated that the mammal may have been floating close to the shore when abnormally high tides picked it up and threw it into the jungle.

"Along with this astonishing feat, we are baffled as to what a humpback whale is doing on the north coast of Brazil during February because this is a very unusual occurrence," he told local media.

He said given humpback whales usually don't travel to the north, it's likely it became separated from its pod during the during the migratory cycle.

The Maritime Herald suggested the animal may have been killed by swallowing marine plastics before the body washed up on shore.