Chinese scientists claim to have changed the genes in human embryos for the first time in history. Although scientists have been manipulating DNA for years, it's been off-limits to make changes in the DNA in an embryo because the changes could be passed to future generations.

Researchers at Sun Yat-sen University in Guangzhou modified a gene responsible for a potentially fatal blood disorder called β-thalassaemia. They used a gene-editing technique known as CRISPR/Cas9 to produce an embryo free of the ailment.

The experiment was published in the journal Protein & Cell, confirming rumors that the experiment had been performed, and immediately sparked concerns.

"I believe this is the first report of CRISPR/Cas9 applied to human pre-implantation embryos and as such the study is a landmark, as well as a cautionary tale," George Daley, a stem-cell biologist at Harvard Medical School in Boston, Massachusetts, told Nature.

"Their study should be a stern warning to any practitioner who thinks the technology is ready for testing to eradicate disease genes."

The Chinese team tried the new technique on 86 single-cell fertilized embryos. After 48 hours, 54 survived. Of those, 28 embryos were found to have been successfully modified. The study was halted due to the low rate of success.

"If you want to do it in normal embryos, you need to be close to 100 percent," researcher Junjiu Huang told Nature. "That's why we stopped. We still think it's too immature."

The Chinese experiments are considered by many to be ethically questionable. Huang tried to blunt criticism by saying that the embryos used were "non-viable," meaning they couldn't result in a live birth.

Some critics said the technique could lead to designer babies with parents picking what they consider to be desirable traits for their children. The techniques to create designer children are being perfected, and some researchers report complete success in creating "designer" mice.

Still, that could be difficult in humans since in many cases no single gene is responsible for a particular trait, and many genes have several functions.

Other critics warned of even more dire consequences, saying that since the genetic changes altered DNA, they can be inherited and have unexpected effects on future generations.

Others put a positive spin on the development saying it could lead to banishing deadly inherited diseases, such as cystic fibrosis or certain cancers. Last year, scientists reported that they cured a genetic liver disease in living mice.