Doctors at Great Ormond Street Hospital are appealing for black, Asian and mixed race bone marrow donors to come forward as they warn non-white children are facing a "needle in a haystack" search for matches.

There are currently 50 times as many white Northern European donors registered in the UK as African-Caribbean donors, nearly 20 times that of south Asian donors, and more than 560 times as many as donors from the Middle East.

The issue will be highlighted in a new series of BBC Two's Great Ormond Street documentary, with tonight's episode focusing on children with rare diseases and following nine-year-old Keano Klein, a young boy from a complex ethnic heritage.

He suffers from a white blood cell deficiency known as severe congenital neutropenia and is in desperate need of a bone marrow transplant.

Keano's lead clinician and director of the bone marrow unit at the London children's hospital, Professor Paul Veys, said: "For children like Keano who have rare conditions affecting their immune systems, a bone marrow transplant is often the only treatment offering them any chance of long-term survival.

"All children who undergo such a transplant face the risk of rejection, the side effects of toxic drugs and a number of other possible complications. But for patients from ethnically-diverse backgrounds, the odds are significantly stacked against them because of a chronic shortage of suitably matched donors."

He said that for every 1,000 white Caucasian donors registered there are only 21 African-Caribbean donors, 53 south Asian donors and two Middle Eastern donors.

While there are 774,518 white Northern European donors registered in the UK, this compares to just 16,009 African-Caribbean donors, 41,355 south Asian donors and 1,374 Middle Eastern donors.

"Finding an unrelated donor match for any child is challenging, but when the pool of donors is so drastically reduced for some children, this clearly puts them at a huge, often life-threatening, disadvantage," Prof Veys added.

He said the number of non-white patients able to be matched to an unrelated donor has shown some improvement since 2010, mainly as a result of improved access to UK-sourced umbilical cord blood donations.

This blood is collected, with parents' consent, from the umbilical cords of newborn babies in NHS maternity units and stored in a bank for use by other patients who may need a match in the future.

People can visit www.nhsbt.nhs.uk/bonemarrow to find out more about becoming a donor.