Gerard Butler is struggling with his emotions as he promotes new movie Machine Gun Preacher - because he finds it hard not to weep during interviews.

The 300 star plays real-life Sudan hero Sam Childers in the film and admits it's becoming difficult for him to recall the time spent on the set of the film in South Africa without crying.

Sobbing during a recent interview with the Los Angeles Times, he explains, "This happened to me a lot when we were filming. I would just be overcome. I feel every emotion. I haven’t talked much about this movie in a while, and I did the other day, and I just started crying. I cried for about five minutes."

Sam Childers transformed his drug-riddled, crime-filled life after finding God and founding an orphanage in war-torn Sudan in 1998.

Gerard Butler adds, "A lot of the feelings I felt with Sam, the violence and the craziness, being out of control and not knowing how to live your life, I had all that. Did I go around stabbing people and shooting people? No. Did I end up in Africa building an orphanage? No. But I did have a massive transformation in my life where I sorted everything out."