Stem cell scientists have for the first time created viable mammalian eggs from scratch in the laboratory and used them to produce healthy offspring.

The research was conducted in mice, but could one day offer new hope to women who have lost their fertility - for instance as a result of cancer treatment.

However, it is likely to be many years before the technique is reliable and safe enough for humans.

Other applications could include shedding further light on the complexities of reproduction, and aiding the conservation of endangered species.

In the experiments, the Japanese team - led by Professor Katsuhiko Hayashi, from Kyushu University - used stem cells both obtained from embryos and generated from mature cells taken from the tips of mouse tails.

The latter were used to create induced pluripotent stem (iPS) cells which have the properties of embryonic stem cells, including the ability to transform into a multitude of different tissues.

Both kinds of stem cell were exposed to specific cocktails of chemicals and biological signals to coax them to develop into eggs.

A key part of the process was mingling the stem cells with "gonadal somatic cells" taken from 12-day-old mouse embryos.

These play an important supporting role in egg development.

Writing in the online edition of Nature journal, the scientists describe how follicles formed spontaneously and surrounded the early stage eggs. The sac-like structures house maturing eggs in the ovaries.

A number of the eggs were eventually fertilised using a standard IVF technique and the resulting embryos produced healthy, fertile offspring.

The success rate was low - just 11 out of 316 two-cell embryos ended up delivering live births. Nevertheless, British scientists working in the same field praised the Japanese achievement.

Professor Richard Anderson, from the University of Edinburgh, said: "This is the first report of anyone being able to develop fully mature and fertilisable eggs in a laboratory setting right through from the earliest stages of oocyte (egg) development ..

"Although we are a long way from making artificial eggs for women at the moment, this study also provides us with a basis for experimental models to explore how eggs develop from other species, including in women.

"This is extremely challenging at the moment due to the difficulties of getting eggs to study."