A cast of one of the largest dinosaurs ever to stride the Earth goes on display in London on Friday, the first time the star exhibit has been seen in Europe since the original was discovered in Patagonia.

At 37.2 metres long, the titanosaur – named Patagotitan mayorum – only just fits into the exhibition hall at London's Natural History Museum.

With its neck extended upwards, it would have been tall enough to poke its head into a five-storey building, according to researchers.

Titanosaurs were the last remaining long-necked sauropod dinosaurs still thriving at the time the species went extinct.

Patagotitan will be a welcome replacement for the museum's longtime dinosaur attraction, the popular Diplodocus "Dippy" replica which was on display until 2017.

The new cast is a replica of one of six titanosaurs found after a farmer in the Argentinian region spotted a giant thigh bone sticking out of the earth in 2010, leading to excavations over a number of years.

"They discovered a graveyard of these animals with six different individuals in the ground," said Paul Barrett, the exhibition's science lead.

"Over about three years, they excavated all these bones... and were able to reveal that they had a new type of gigantic dinosaur... one of the largest animals that's ever walked the Earth," he added.

The titanosaurs lived in the forests of modern-day Patagonia 100 to 95 million years ago during the Late Cretaceous period.

Researchers estimate that in addition to its extraordinary length, it would also have weighed about 57 tonnes.

The recently discovered herbivore would have had four column-like legs, and an extremely long neck and tail.

All six dinosaurs, which were discovered at the same site, are believed to have died at the same time although the reason for their demise remains a mystery. (AFP)