A Chinese scientist at the centre of an ethical storm over what he claims are the world's first genetically edited babies said on Wednesday he is proud of his work and that another volunteer is pregnant as part of the research.

He Jiankui, an associate professor at Southern University of Science and Technology in Shenzhen, China, addressed a packed hall of around 700 people attending the Human Genome Editing Summit at the University of Hong Kong.

"For this case, I feel proud. I feel proudest," He said, when challenged by several peers at the conference.

"This study has been submitted to a scientific journal for review," He said. He did not name the journal and said his university was unaware of his study.

He, who said his work was self-funded, shrugged off concerns that the research was conducted in secrecy, explaining that he had engaged the scientific community over the past three years.

In videos posted online this week, He said he used a gene-editing technology known as CRISPR-Cas9 to alter the embryonic genes of twin girls born this month.

A microplate containing embryos that have been injected with Cas9 protein, in a laboratory in Shenzhen on Oct. 9. (Mark Schiefelbein/Associated Press)

He said gene editing would help protect the girls from infection with HIV, the virus that causes AIDS. He said eight couples were initially enrolled for his study while one dropped out. The criteria required the father to be HIV-positive and the mother to be HIV-negative.

He claimed his results could be used for millions with inherent diseases, adding that he would monitor the two newborns for the next 18 years and hoped they would support continued monitoring thereafter.

'Irresponsible' use of gene-editing technology

Scientists and the Chinese government have denounced the work that He said he carried out, and a hospital linked to his research suggested its ethical approval had been forged.

China's National Health Commission has ordered local officials in Guangdong province to investigate He's actions, and his employer, Southern University of Science and Technology of China, is investigating as well, The Associated Press reported.

The conference moderator, Robin Lovell-Badge, said the summit organizers were unaware of the story until it broke this week.

CRISPR-Cas9 is a technology that allows scientists to essentially cut and paste DNA, raising hope of genetic fixes for disease. However, there are concerns about safety and ethics.

The Chinese Society for Cell Biology in a statement on Tuesday strongly condemned any application of gene editing on human embryos for reproductive purposes and said that it was against the law and medical ethics of China.

More than 100 scientists, most in China, said in an open letter on Tuesday the use of CRISPR-Cas9 technology to edit the genes of human embryos was dangerous and unjustified. "Pandora's box has been opened," they said.

After He spoke, David Baltimore, a Nobel laureate from the California Institute of Technology and a leader of the conference, said He's work would "be considered irresponsible" because it did not meet criteria many scientists agreed on several years ago before gene editing could be considered.

"I personally don't think that it was medically necessary. The choice of the diseases that we heard discussions about earlier today are much more pressing" than trying to prevent HIV infection this way, he said.

Together CRISPR and Cas-9 act as molecular scissors and a guide to cut and paste genetic material. (CBC)

If gene editing is ever allowed, many scientists have said it should be reserved to treat and prevent serious inherited disorders with no good alternatives, such as sickle cell anemia and Huntington's disease. HIV is not an appropriate candidate because there are already safe ways to prevent transmission and, if contracted, it can be kept under control with medications, researchers said.

The case shows "there has been a failure of self-regulation by the scientific community" and said the conference committee would meet and issue a statement on Thursday about the future of the field, Baltimore said.

Approval 'suspected to have been forged'

The U.S. National Institutes of Health said Wednesday there should be international intervention.

"Without such limits, the world will face the serious risk of a deluge of similarly ill-considered and unethical projects," the agency said in a statement.

Meanwhile, more American scientists said they had contact with He and were aware of or suspected what he was doing, The Associated Press reported.

Dr. Matthew Porteus, a genetics researcher at Stanford University, where He did postdoctoral research, said He told him in February that he intended to try human gene editing. Porteus said he discouraged He and told him "that it was irresponsible, that he could risk the entire field of gene editing by doing this in a cavalier fashion."

Dr. William Hurlbut, a Stanford ethicist, said he has "spent many hours" talking with He over the last two years about situations where gene editing might be appropriate.

"I knew his early work. I knew where he was heading," Hurlbut said. When Hurlbut saw He four or five weeks ago, He did not say he had tried or achieved pregnancy with edited embryos, but "I strongly suspected" it, Hurlbut said.

"I disagree with the notion of stepping out of the general consensus of the scientific community," Hurlbut said. If the science is not considered ready or safe enough, "it's going to create misunderstanding, discordance and distrust."

Shenzhen Harmonicare Medical Holdings Limited, reported by media as being involved in He's project, sought to distance itself by stating the hospital never participated in any operations relating to the gene-edited babies and no related delivery had taken place.

In a statement published to the Hong Kong stock exchange on Tuesday, the group said preliminary investigations indicated the signatures on the application form circulated on the internet are "suspected to have been forged, and no relevant meeting of the medical ethics committee of the hospital, in fact, took place."

He's research focuses on genome sequencing technology, bioinformatics and genome editing, according to his biography on the Human Genome Editing Summit's website.

He received his PhD at Rice University in Houston, Texas, and worked as a postdoctoral research fellow in Stephen Quake lab at Stanford University, according to the site.