Rupert Murdoch says the "momentous" decision to sell $US52.4 billion ($68 billion) of 21st Century Fox's assets to rival Walt Disney after building a global empire from a "single newspaper in Adelaide" 65 years ago reflects the need to respond to rapid change in technology and competitors transforming the media landscape.

The historic deal to divest about two-thirds of the family's total media interests including Hollywood movie production studio and international television arms will leave the self-described "news man with a competitive spirit" to focus on news and live sport at a slimmed down "new Fox" and sister publisher News Corporation.