'Dammit Hydra': Supervillains blamed for Avengers 2 trailer leak

The trailer for one of the most hotly-anticipated superhero movies ever has been leaked online a week early, and you might be surprised who's being blamed.

The first teaser trailer for Avengers: Age of Ultron was meant to air for the first time next Wednesday.

Producers Marvel Studios had planned to use the trailer as a cross-promotion to entice people to tune in to their related TV show, Marvel's Agents of S.H.I.E.L.D.

However, the first look at the new movie was splashed across the internet today.

Marvel responded in typical tongue-in-cheek style, tweeting "Dammit, Hydra" - referring to a villainous organisation that feature as antagonists in the company's comics as well as its movies and TV shows.

The entertainment giant then decided to keep the cat out of the bag and "officially" released the trailer a week early.

Fans get a first look at James Spader's chilling performance as Ultron, a genocidal robot who will be the film's main antagonist.

The movie appears to be going for a darker tone than its blockbuster predecessor, which raked in more than US$1 billion in ticket sales.

"This is the end," Robert Downey Jr's Tony Stark says at one point.

"It's the end of the path I started us on."

However, with Avengers 3 already scheduled along with a huge slate of intertwined Marvel films for years to come, it appears unlikely that the "end" will be coming anytime soon.