There need to be tighter regulations to protect patients who are considering "stem cell tourism", a team of experts have said.

Hundreds of clinics around the world are offering therapies that claim to offer the transplantation of stem cells.

Medical centres are marketing the therapy as a way to repair damaged tissues for a range of conditions, including multiple sclerosis and Parkinson's disease.

Often these therapies are advertised with the promise of a cure.

Based on these pledges, some patients are travelling to other countries where medical regulations are less strict for treatment with potentially unsafe therapies, an international team of experts warned.

Writing in the journal Science Translational Medicine, the group said there was often no evidence to show the treatments helped anyone, or would not cause harm.

They raised concerns that the practice risked undermining the development of validated therapies and put lives at risk.

The group, which includes experts from the University of Edinburgh, has called for the World Health Organisation to help guide responsible clinical use of cells and tissues.

It has also called for tighter regulation on advertising so that unscrupulous claims do not go unchallenged.

The article called for regulatory authorities from around the world to agree international standards for the manufacture and testing of cell and tissue-based therapies.

"Many patients feel that potential cures are being held back by red tape and lengthy approval processes," said Dr Sarah Chan, a chancellor's fellow at the University of Edinburgh.

"Although this can be frustrating, these procedures are there to protect patients from undergoing needless treatments that could put their lives at risk.

"Stem cell therapies hold a lot of promise but we need rigorous clinical trials and regulatory processes to determine whether a proposed treatment is safe, effective and better than existing treatments."

Some types of stem cell transplantation have been approved to treat certain types of cancer and to grow skin grafts for patients with severe burns.