LONDON - Canadian James Cameron's sci-fi extravaganza "Avatar" is getting its first airing before a mass audience in London.

Stars Sigourney Weaver, Sam Worthington and Zoe Saldana are expected to join the crowds in London's Leicester Square for today's premiere.

The 3D epic about humans taking extraterrestrial form as they explore a distant world is reportedly one of the most expensive movies ever made. It uses cutting-edge digital technology to create dizzying special effects.

The film industry is watching closely to see how audiences respond to Cameron's first narrative film in 12 years. The director is hoping for a hit to match his 1997 blockbuster "Titanic," which has taken $1.8 billion worldwide at the box office.

"Avatar" opens around the world next week.