A British schoolboy is to portray the voice of God in upcoming epic Exodus: God and Kings.

Director Ridley Scott told The Hollywood Reporter that he has used various means to depict God's communication with Moses, but face-to-face encounter comes in the form of a young boy, Malak, played by 11-year-old British actor Isaac Andrews.

Moses, played by Christian Bale, first meets Malak at the burning bush (Exodus chapter 3). The boy then appears several times throughout the film to guide and grapple with him. Malak means "messenger" in Hebew, and Moses comes to understand that the boy is being used by God to speak to him.

"Sacred texts give no specific depiction of God, so for centuries artists and filmmakers have had to choose their own visual depiction," Scott said.

"Malak exudes innocence and purity, and those two qualities are extremely powerful."

The movie is set to do well when it is released in December, but there has been much discussion over how accurate to the original text the final cut will be.

Scott has described Moses' story as "one of the greatest adventures and spiritual experiences that could ever have been," but critics have expressed concern that attempts to adapt the movie to fit Hollywood's standards will mean key details are lost.

Attracting particular interest has been the revelation that in the film, it is not God who parts the Red Sea, but an earthquake.

"You can't just do a giant parting, with walls of water trembling while people ride between them," Scott said in an interview with Entertainment Weekly.

"I didn't believe it...when I was just a kid sitting in the third row. I remember that feeling, and thought that I'd better come up with a more scientific or natural explanation."

Bale has also slammed his character as "barbaric". "I think the man was likely schizophrenic and was one of the most barbaric individuals that I ever read about in my life," he said of Moses.