Australian actor Chris Hemsworth has shed his galactic superhero physique in a dramatic transformation for his upcoming movie, In the Heart of the Sea.

The heartthrob, well-known for his early role on Home and Away and more recent roles in the blockbuster Thor and Avengers movies, shared a photo of his new look on Twitter on Sunday.

While still rugged and long-haired, Hemsworth is no longer recognisable as the Asgard king.

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Instead, the photo shows Hemsworth sporting a shaggy mop of hair, a shaggier beard, protruding ribs and some scabbing fake sunburn.

“Just tried a new diet/training program called ‘lost at sea’. Wouldn’t recommend it,” he said.

In a live Q&A on Twitter on Sunday night, Hemsworth told a fan that losing the weight was the most challenging part of filming In the Heart of the Sea.

The film, due to hit cinemas in December, tells the story of the crew onboard the American whaling ship, Essex, which sunk after being attacked by a sperm whale in 1820.

Sinking 3700 kilometres off the coast of South America, the attack left the crew stranded at sea for 90 days.

The ordeal famously forced the crew to resort to cannibalism to survive and provided the inspiration for Herman Melville’s classic novel, Moby Dick.

While Hemsworth’s role as first mate Owen Chase may have required him to shed kilograms, there is no sign of him having shed his Australian humour.

Hemsworth was asked on Twitter which of his previous roles would make the best company if he was truly stranded at sea.

“Thor, so we could fly the hell away from there,” he replied.

Just tried a new diet/training program called “Lost At Sea”. Wouldn’t recommend it.. #IntheHeartoftheSeapic.twitter.com/y89McNuiiV

— Chris Hemsworth (@chrishemsworth) November 22, 2015

-ABC