City of Ember, featuring Bill Murray and 14-year-old Oscar nominee Saoirse Ronan, has premiered in the US.

In the fantasy film, two teenagers embark on an adventure to find their way out of their dying underground city.

The role was a challenging one for such a young actress but Ronan said working along side her co-star Harry Treadaway made it easier.

She said: "I really get on well with Harry. We're like that, he kind of became my big brother."

She recently finished working on the film, The Lovely Bones, with actress Susan Sarandon, whom she said she looks up to.

Murray also revealed he is thinking about being involved in a third Ghostbusters movie.

He said: "If the script's good, I'm not going to get sentimental about it. I really liked the first one and then we did a second one.

"I really liked the first one better. So the idea that you do a third one, it would really have to be pretty good. Everyone's on their own so we'll see."

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