China has shocked the world and has since been ordered to "rein in" its scientists who have edited the DNA of human embryos for the first time, a practice that has been banned in many parts of the world.

For the first time ever, researchers at the Sun Yat-sen University in Guangzhou confirmed they had engineered human embryos to modify the gene responsible for the fatal blood disorder thalassaemia.

The team that was led by Junjiu Huang attempted to head off fears of eugenics by claiming that the embryos themselves were "non-viable" and could never have become babies. 

But critics warned that China was becoming the "Wild West" of genetic engineering, where research stating that this was a first step towards designer children called for a ban of the practice worldwide.

"This news emphasises the need for an immediate global ban on the creation of GM designer babies," said Human Genetics Alert Director, Dr David King. "It is critical that we avoid a eugenic future in which the rich can buy themselves a baby with built-in genetic advantages."

"It is entirely unnecessary since there are already many ethical ways to avoid thalassaemia. This research is a classic example of scientific careerism - assuring one's place in the history books even though the research is unnecessary and unethical."

The Chinese team used embryos they obtained from fertility clinics that had been created for use in IVF but had an extra set of chromosomes, following fertilization by two sperm, which prevents a live birth. 

They injected 86 embryos with the Cas9 protein and left them for two days to allow the gene-editing to take place.  Of the 71 that survived, 54 were genetically tested.  The testing revealed that just 28 were successfully spliced and only a fraction of those contained the replacement genetic material.  They also discovered a number of unexpected mutations in genes which should not have been effected.

British scientists said that no more experiments should be carried out until an international agreement on whether the technique was both safe and ethical had been reached.

Professor Shirley Hodgson, Professor of Cancer Genetics, St. George's University of London, said, "I think that this is a significant departure from currently accepted research practice. Can we be certain that the embryos that the researchers were working on were indeed non-viable?  Any proposal to do germline genetic manipulation should be very carefully considered by international regulatory bodies before it should be considered as a serious research prospect."

Dr. Philippa Brice, of the health policy think-tank the PHG Foundation, added, "This story underlines the urgent necessity for international dialogue over the ethics of germline gene editing in human embryos, well in advance of any progression towards theoretical clinical application.  Recent calls for a moratorium on any such research to allow time for expert and public consideration of what is and is not ethically, socially and indeed legally acceptable with respect to human germline genetic modification should definitely be heeded."

While Huang has said he has abandoned the project, at least four groups in China are believed to be currently working on genetically modifying human embryos.