Pacific Rim cast struggled with physically-demanding shoot

Charlie Hunnam and his Pacific Rim castmates were forced to put their endurance to the test while filming the new science-fiction epic because the shoot was so physically-demanding.

In the film, directed by Guillermo del Toro, Rinko Kikuchi and the Sons of Anarchy star are forced to save mankind from an invasion of giant monsters by suiting up as oversized robots to do battle.

The stars were locked into 20 ton metal contraptions for hours at a time and del Toro admits the entire cast had difficulty adjusting to the armour.

He tells the New York Daily News, "We built that machine for real and it weighs several tons and at least a couple of hundred pounds of that weight was resting on the actors' shoulders. We saw every one of the actors break down on that set, except for the female lead actress Rinko Kikuchi. She's the only actor that didn't snap."

Meanwhile, the Japanese actress insists she struggled through the scenes just as much as the others: "It was the most physically demanding shoot of my career."

And Hunnam adds, "We all ended up crumbling under the strain."