Scientists in the United States are trying to grow human organs inside pigs - but animal rights activists say it will create a science-fiction form of animal cruelty.

LISTEN ABOVE: Peter Stevenson talks to Rachel Smalley

The scientists have successfully injected human stem cells into pig embryos - it's part of research aimed at overcoming the worldwide shortage of transplant organs.

But Peter Stevenson from Compassion in World Farming told Rachel Smalley there are other ways, and we should be focusing our resources on them:

"I fully understand the longing of ill people and their families for transplant organs, but I am very concerned about the opening up of a new source of animal suffering particularly when there's a much better solution.

"A lot of genetically engineered animals will die in the very early stages of life from breathing difficulties from heart problems. There can be problems even earlier at the experimental stage."

Mr Stevenson said a law change to assume people will donate their organs upon death unless they opt out, would save many lives.