The Chinese scientist who claims to have altered the DNA of twin girls before birth – without going through the usual scientific channels – said he was proud of his work, and claimed another woman enrolled in his trial was pregnant with a similarly modified baby.

The scientist, He Jiankui, spoke to hundreds of colleagues and journalists on Wednesday at the International Human Genome Editing Summit at the University of Hong Kong.

He said details of the first births from the trial, which used gene-editing technology known as Crispr-Cas9, had been submitted to a scientific journal, which he did not name. Nor did he say when the results might be published.

In a planned presentation, He, an associate professor at Southern University of Science and Technology, in Shenzhen, described how he used Crispr-Cas9 to modify a gene called CCR5 in a number of embryos created through IVF for couples with HIV-positive fathers.

The modification was intended to mirror a natural mutation found in a small percentage of people which makes them resistant to the virus. Two girls named Nana and Lulu were born with the genetic changes, he said.

The researcher’s 40-minute Q&A offered a charged forum for scientists to publicly question a colleague caught in controversy.

The Nobel laureate David Baltimore, an organiser of the summit, who is professor emeritus of biology at the California Institute of Technology, called He’s work irresponsible. “I think there has been a failure of self regulation by the scientific community because of a lack of transparency,” Baltimore said.

David Liu, a biologist at the Broad Institute in Cambridge, Massachusetts, challenged He on how the girls might benefit from having their DNA altered. The children were not at risk of contracting HIV at birth and he said there were many ways to avoid HIV infection later in life. “What was the unmet medical need for these patients in particular?” Liu asked.

He said in defence: “I truly believe that, not only for this case but for millions of children, they need this protection since an HIV vaccine is not available. For this case I feel proud.”

Matthew Porteus, professor of paediatrics at Stanford University, said: “He’s already at risk of becoming a pariah.” Scientists talked about their research plans years in advance with many colleagues, to get feedback before they set out. “Unless he starts to engage in the scientific process, it will get worse and worse,” Porteus added.

At the summit He presented slides to an audience of scientists who expressed concern that he could have brought harm to his subjects and jeopardised gene editing research.

The scientist said, however, he wanted to prevent HIV being inherited from a parent because so many children were affected by the virus in China. Eight couples had agreed to take part in the study, though one had dropped out. With each, the father was HIV positive, while the woman was clear of the virus.

He told the audience he had worked on 31 eggs and implanted two altered embryos in one woman. One of the babies had only one copy of the CCR5 gene edited, which was not enough to confer HIV resistance. The health of both children would be monitored for the next 18 years.

The gene-editing work had started three years ago, partly paid for by He, who had consulted, he said, with just a few colleagues about his plans.

In the UK and many other countries it is illegal to create genetically modified babies, and scientists in the field have reached a broad consensus that it would be deeply unethical to try. Genome editing is not considered safe, and any genetic modifications – whether beneficial or unintentionally harmful – affect not only the child, but their children and future generations.

“It is impossible to overstate how irresponsible, unethical and dangerous this is at the moment,” said Kathy Niakan, a scientist at the Francis Crick Institute, in London, who was present at the summit. “There was a worrying lack of oversight or scrutiny of his clinical plans before he started human experiments and a complete lack of transparency throughout the process.

“I found it highly troubling that He avoided questions about approval processes, and his answers on patient recruitment and consent did not reassure me. The team don’t seem to have had adequate training on proper consent processes. Offering vulnerable patients free IVF treatment presents a clear conflict of interest.”

On Tuesday it was announced that He’s work was being investigated by Chinese officials and his university in Shenzhen.

He’s vague answers at the summit prompted more questions from the audience. Did He know enough about the technology to ensure that the children would be healthy, or might they contract other deadly viruses? He insisted he did know enough.

“How do you see your responsibility to these children?” asked Eben Kirksey, an associate professor of anthropology, at Deakin University, in Victoria, Australia. He replied that the children’s medical care would be provided for, but offered no details.

The missing information frustrated many in the audience. “This is a red line,” one conference attendee told He. “Why did you choose to cross it and conduct this in secret?”

Robin Lovell-Badge, a geneticist at the Francis Crick Institute, in London, claimed that He was misguided. “He clearly made some wrong decisions. I’m very critical of calling this a scientific breakthrough because he’s messed up all along.”

Lovell-Badge said he was inclined to believe that He had altered the babies’ DNA, but said the scientist needed to show proof of it. The only way to convince the world would be if an independent, qualified, lab tested the DNA of the parents and the two babies to show that the genes had been edited. “Nothing that I’ve been shown says it’s false. But the evidence I’ve seen is not yet good enough,” he added.