Supporters say research could be vital first step towards growing organs that can then be transplanted into people in need

Human-animal hybrids are to be developed in embryo form in Japan after the government approved controversial stem-cell research.

Human cells will be grown in rat and mouse embryos, then brought to term in a surrogate animal, as part of experiments set to be carried out at the University of Tokyo.

Supporters say the work – led by renowned geneticist Hiromitsu Nakauchi – could be a vital first step towards eventually growing organs that can then be transplanted into people in need.

But opponents have raised concerns that scientists are playing God.

They worry the human cells could stray beyond the targeted organs into other areas of the animal, effectively creating a creature that is part animal, part person.