They believe the discovery marks the start of a revolution in the treatment of ageing, infertility, cancer, heart disease and a host of degenerative illnesses such as Alzheimer's and Parkinson's disease.
After a 20-year race to find the embryonic "stem cells", which are able to develop into any human tissue whether it is blood, muscle, skin, bone or nerves, several teams of scientists are claiming they have identified and grown the elusive progenitors of the human body.
The find "opens the possibility for some dramatic new transplantation therapies", said James Thompson, a developmental biologist at the University of Wisconsin-Madison and a member of one of the scientific teams.
It could enable scientists to grow from scratch unlimited quantities of body components such as heart muscle, bone marrow or brain tissue.
The stem cells might also provide scientists with new ways of developing drugs specifically directed at individual patients as well as treating inherited disorders by transplanting custom-designed tissue that has been genetically engineered.
"Although a great deal of basic research needs to be done before these cells can lead to human therapies, I believe that in the long run they will revolutionise many aspects of transplantation medicine," Professor Thompson said.
At least three teams of scientists are now claiming to have isolated and grown human stem cells from early embryos, which were created either by in vitro fertilisation or had been aborted for other reasons.
Professor Thompson's group, which is funded by the Geron Corporation, an American biotechnology company researching into anti-ageing treatments, publishes its findings in the journal Science.
Another group, led by John Gearhart of Johns Hopkins University School of Medicine in Baltimore, publishes its findings next week in the Proceedings of the National Academy of Sciences and a third group, led by Evan Snyder of Harvard University, publishes its work in the current issue of Nature Genetics.
Geron said the stem cells derive from early human embryos at the "blastocyst" stage of development, when they consist of a hollow ball of 140 cells a few days after fertilisation.
Professor Thompson's team has shown that the stem cells can be stimulated to grow into three basic categories of embryonic material and subsequently into any one of a number of adult tissues, such as cartilage, bone, muscle, nerve and gut cells.
"Our hope is that these cells could be grown in the laboratory and then used to regenerate failing tissue," said Thomas Okarma, the vice-president of research and development at Geron.
"Because these cells do not age, they could be used to generate virtually a limitless supply of cells and tissues for transplantation," he said.
Geron is hoping to cash in on the breakthrough to develop ways of combating age-related degenerative diseases.