An anonymous British blood donor has come forward to help with Zainab Mughal's treatment in the US.

Three matching donors were located in the global effort to help save the life of the two-year-old cancer patient who needs some of the rarest blood in the world.

Zainab Mughal, from Florida, has a neuroblastoma - an aggressive form of cancer - and requires two bone marrow transplants and a series of transfusions to restore her blood supply while undergoing chemotherapy.

The donor, a mother-of-two from Nottingham, said she felt "humbled" to be playing a small role in the two-year-old's treatment.

Twitter @my1blood

"I do hope the publicity encourages more people to donate, especially from the Asian community," she told the BBC.

"Even a single donation can make a massive difference to someone who needs it."

Last week OneBlood, a not-for-profit organisation, launched a global search to find compatible donors in a race-against-time battle to save the toddler's life.

Victoria Police even joined the efforts by retweeting a tweet sent by the Australian Red Cross Blood Service.

A global blood search is underway to save the life of a two-year-old girl. Are you a match? You must be exclusively of Pakistani, Indian or Iranian descent, be blood type 'O' or 'A' and donations must be coordinated with @my1blood in advance.https://t.co/gbVCtDDv2J — Red Cross Blood Au (@redcrossbloodau) December 6, 2018

To be a compatible donor, people must be of Pakistani, Indian or Iranian descent and have type 'O' or 'A" blood. They also must be missing a specific blood antigen like Zainab.

So far, three matching donors have been located, including a donor located in the United Kingdom. The other two matching donors are from the United States.

OneBlood said the response from the public has been "unprecedented", but additional donors are still needed.

"Zainab will need blood transfusions for the foreseeable future. To support her long-term blood needs, the search is on to find at least seven to ten compatible donors," it says on the OneBlood website.

Zainab's blood is missing a common antigen, known as the Indian-B Antigen.

This is the reason why it's that much more difficult to find someone else who's blood is also missing the Indian-B Antigen.

Read more Global blood search underway to save the life of two-year-old girl

The bottom line is, for a donor to be a match they must be a certain blood type and also be missing the Indian-B Antigen or the little girl's body will reject the blood, says US organisation OneBlood.

"Because she's made this antibody we now have to provide more specially matched blood for this child," said Frieda Bright, OneBlood's reference lab manager.

The blood also needs to come from a very specific population - people from Iran, Pakistan and India.

"The possibility of us finding a compatible donor within the right ethnic group we want to screen is less than four per cent," said Ms Bright.

"We have a zero per cent chance of finding compatible blood for this little girl if we look in pretty much any other ethnic group."