A team has grown hybrid embryos after injecting human DNA into eggs taken from cows' ovaries, which had most of their genetic material removed.

The embryos survived for three days and are intended to provide a limitless supply of stem cells to develop therapies for diseases such as Alzheimer's, Parkinson's and spinal cord injuries, overcoming a worldwide shortfall in human embryos.

Dr Teija Peura, director of human embryonic stem cell laboratories at the Australian Stem Cell Centre, said somatic cell nuclear transfer (SCNT) had been done between animal species, but the "99 per cent human" embryos could boost research.

"If successful, they would provide an important additional research tool to help realisation of stem cell-based therapies for human diseases," Dr Peura said.

"All avenues of research, including SCNT . . . need to be encouraged if we want to fulfil the promises of stem cell technologies."

But her colleague, Dr Andrew Laslett, warned the process was yet to yield a stem cell line and so it remained only an academic possibility.

In January, the Fertilisation and Embryology Authority gave Newcastle University a licence to do the work, but the British Parliament would debate the longer-term future of such research next month.

Under the licence, embryos are not allowed to be developed beyond 14 days.

Preliminary findings of the embryo program were presented in Israel last week, and the head of the university's Institute of Human Genetics, Prof John Burn, said further evaluation would be done before the full details were published.

"If the team can produce cells which will survive in culture, it will open the door to a better understanding of disease processes without having to use precious human eggs," Prof Burn said.

"Cells grown using animal eggs cannot be used to treat patients on safety grounds, but they will help bring nearer the day when new stem cell therapies are available."

The Catholic Church in Britain branded the creations as "monstrous" - a view supported by Caroline Chisholm Centre for Health Ethics director Fr Kevin McGovern.

"An almost-human embryo is being created and then it's being destroyed," he said.

"I cannot see that that respects human life or the dignity of human life.

"Human beings - or even almost human embryos - are not just things that you can use in a laboratory experiment.

"What is being created is life.

"No one knows exactly what would grow from these embryos.

"If this is approved in the UK, there will be renewed pressure to permit it here, and we will travel further down the slippery slope of allowing just about anything."

It is not the first time hybrids have been created.

The method was pioneered by Dr Hui Zhen Sheng's team at the Shanghai Second Medical University, China, where she fused human cells with rabbit eggs to produce early stage embryos, which in turn yielded human stem cells.

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