Sigourney Weaver in town for Avatar premiere

London is at the eye of the Avatar storm. The first public screening of the new James Cameron movie is to take place not in Los Angeles but in London tonight. Sigourney Weaver is expected to be joined by co-stars Sam Worthington and Zoe Saldana for the Leicester Square red-carpet premiere of the 20th Century Fox movie.

Hollywood will be watching anxiously: this is Cameron's first big film in 12 years since his blockbuster Titanic, starring Leonardo DiCaprio and Kate Winslet, took a staggering $1.8bn at the box office worldwide. It became the most successful movie in the history of filmmaking, a record it still holds.

Much has altered on the Hollywood landscape since 1997. After a period of strikes, recession and executive sackings as traditional movies have been overtaken by ever-more interactive computer games, the studios need to know whether a good old-fashioned blockbuster - albeit in state-of-the-art 3D - can still win a worldwide audience and make its producers a fortune.

By now, anyone who opens a magazine or visits a movie website regularly is aware of the blue creatures who populate Cameron's sci-fi extravaganza. But we don't know much more than the basic plot line: humans' avatars are sent to a distant moon, Pandora, to infiltrate the blue-skinned Na'vi polulation.

We also know that the digital effects have made it one of the most expensive films ever and that it's 161 minutes long - though that's still half an hour shorter than the truly epic Titanic.

Finally, we also know that Sigourney Weaver, who plays scientist Grace Augustine, cried after she saw the film for the first time.

"It will pick you up and shake you like a little rag doll," she told the Guardian. "I'm not too much of an emotional creature, but I was weeping by the end. I remember reading the script and thinking, 'I love this but how can he ever do this?'. Nothing like this has been done before - floating mountains!"

Avatar opens worldwide on December 17 but we can expect early reviews overnight following this evening's premiere. Watch this space.