Spider-Man star Tobey Maguire said the film would be 'open-ended'

"There will be some conclusions, though I wouldn't say it's necessarily the end," he told fans in California.

The first set of unfinished footage shows the movie mixing live action with animation and computer graphics.

It also offers brief glimpses of actors Topher Grace and Thomas Haden Church as villains Venom and Sandman.

'Way better'

At comic book convention Comic-Con in San Diego, California, Maguire said Spider-Man 3 would be left "open-ended".

"If there are stories worth telling, then we'll tell them," he said.

Director Sam Raimi said that as a long-time comic book fan it had been a "super-dream" to make the Spider-Man films.

But it was also a "great responsibility to tell the story of this character that kids look up to as this great hero", he said.

Sam Raimi hasn't disappointed us yet Spider-Man fan Nora McGuirk

"Certainly you don't want to make anything that isn't worthy of their admiration."

Fans at the convention responded enthusiastically to the new footage.

"It was way better than I expected because you got to see Venom. He looked awesome," said John McCracken, 22.

Nora McGuirk, 26, said: "Sam Raimi hasn't disappointed us yet.

New villains

"He made the entire world happy by putting Venom in it," the manager of Beach Ball Comics in Anaheim added.

Grace said his character, who is a spider-like villain, is "kind of a case study in if someone very similar to Peter [Parker] got the same powers but didn't have a good upbringing".

Raimi also revealed that Harry Osborn would become a villain in the third instalment.

The character is to take on some of the powers of his father, the Green Goblin, the Willem Dafoe character who died in the first film.