Actress Kristen Stewart arrives for the UK premiere of "Twilight" in London's Leicester Square December 3, 2008.[Agencies]

SAN DIEGO - It seems the sun has barely set on the movie phenomenon "Twilight,' and already its sequel "New Moon" is rising with its stars promising a more emotional journey and more action than the first film.

Fans of the original that has raked in more than $380 million at worldwide box offices got their first glimpse of "The Twilight Saga: New Moon" at the giant Comic-Con International pop culture convention in San Diego on Thursday.

Actress Kristen Stewart called the sequel to last November's smash hit "a severely emotional movie" in which her character, teenager Bella Swan, is forced to mature through a series of events that imperil not only her, but her vampire love Edward Cullen.

Co-star Taylor Lautner promised "double the action than there was before," and said he has packed on the muscle to play werewolf Jacob Black, who befriends and protects Bella.

"I changed a lot to portray him correctly," Lautner told reporters ahead of a screening of film footage. "I hit the gym, got a personal trainer, ate good foods, cut out the sugars."

The added heft was critical to his retaining the role of Black after speculation surfaced on the Internet that the film's producers were undecided on bringing him back. But a grass-roots campaign by fans kept him in the picture.

The "Twilight" films, based on a series of best-selling romance novels by Stephenie Meyer, were virtually unheard of by all but loyal and mostly young female fans at this time last year when the first film was promoted at Comic-Con.

But those fans turned out in droves when the film opened in November 2008 and propelled it to No. 1 at U.S. box offices, and the stars thanked the Comic-Con conventioneers for giving it the boost it needed to crossover to mainstream moviegoers.

"Comic-Con was the eye opener, and it just keeps getting bigger," said Pattinson.

"New Moon," which is set for release on November 20, has Bella maturing into adulthood. She is no longer with her love Edward, and her friendship with Black has grown deeper. But events soon bring the two lovers back together.

"There was more to think about," said Stewart about portraying Bella. "It was a more mature part. She's older and has more to deal with.

A line of fans waiting to see footage of the new movie snaked its way around the hallways of the San Diego Convention Center where Comic-Con is being held, and Lautner took note.

"They have the same, if not more, amount of passion and dedication as last year," he said of the fans. "I'm a little nervous, but it's good."