Kristen Stewart felt like a "sports car" after her transformation into an onscreen vampire.

The actress plays Bella Swan in the popular Twilight franchise. Bella changes from a human to a bloodsucking creature in the final instalments of the series.

The brunette star has joked she was eager to try out her new vampire powers on set.

"I felt like, Wow, I'm a sports car. Let's break it in!' Especially in the original Twilight book, my favourite part is when someone says 'Break her in, man!' Let's see what she can do!'" she said at the Comic-Con press conference for the final Twilight movie, Breaking Dawn: Part 2.

Kristen and her co-star Robert Pattinson who plays Bella's husband Edward Cullen - also joked their characters could easily misuse their extraordinary powers if they had a marital dispute.

Vampires are often described as being super-fast and inhumanely strong.

When Robert was quizzed on ideas for a future Twilight plotline, he was quick to make a suggestion.

"What about Edward and Bella getting divorced, and it's a Mr. and Mrs. Smith thing?" he said.

"I could totally rip his head off!" Kristen jokingly added.