Helen Golder, 33, had spent a week at the cardiac care centre for children set up by Chain of Hope
Helen Golder, 33, a nurse at the Royal Brompton and Harefield NHS Trust, and Liz Callan, 31, from Great Ormond Street Hospital for Children, both in London, died at the scene of the accident on Saturday outside the Mozambique capital Maputo.
A third nurse, 32-year-old Susan Andrews, of Frenchay Hospital, Bristol, lost her fight for life today after being flown to Johannesburg, South Africa, for treatment.
The women had just completed a week working for free providing intensive care for sick children in Maputo, on a mission led by heart surgeon Professor Sir Magdi Yacoub.
They were on their way for a day trip to the Kruger National Park in South Africa when their bus was involved in an accident.
According to reports, a tyre is believed to have blown, sending the bus veering into another vehicle.
The Chain of Hope charity, of which Professor Sir Magdi is founder and president, provides children suffering from life-threatening disease with the corrective surgery and treatment to which they do not have access.
The charity's Emma Scanlan said: "It is just tragic. They were people who were helping to save other people's lives and then this happened."
A statement from the charity expressed deepest sympathies to the families and friends of the women.
It said: "All three volunteers had been part of the Chain of Hope medical team that had helped to treat over 17 patients in the Maputo Heart Institute, Maputo, Mozambique.
"The girls were tragically involved in an accident involving a tour bus that was headed for Kruger National Park the day after the charity mission had finished.
"Chain of Hope was proud to have worked with such caring and dedicated professionals who selflessly gave their time and skills to help treat children in need.
"They all shared a very high level of commitment and dedication and were an inspiration to all those they met."
Tributes poured in as news of their deaths reached home.
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Helen (right) worked in the paediatric intensive care unit at Royal Brompton and Harefield NHS Trust
The hospitals in Britain where the women worked sent condolences to their families and paid tribute to their work.
Dr Allan Goldman, of Great Ormond Street Hospital for Children, expressed condolences to the husband and family of Miss Callan, whose married named was Liz Wilson.
He said: "Liz was tragically killed in Mozambique following a Chain of Hope charity mission.
"Giving up her time to help others in this way exemplifies Liz's character as a caring, giving and selfless person.
"Liz had a huge heart, was always smiling and was full of love for life and all those around her.
"She was calm in a crisis, and used her northern humour to get us all through impossible situations.
"Liz was an enormously respected and talented Children's ICU nurse who led by example.
"Both professionally and personally she leaves a huge gap in all our lives.
"We would also like to extend our deepest sympathy to the families of the other nurses who were involved in this tragic accident."
Dr Duncan Macrae, director of paediatric intensive care at Royal Brompton Hospital, paid tribute to Miss Golder, who was originally from Preston, Lancashire.
He said: "Helen was a highly-respected member of the paediatric intensive care nursing team, and was particularly known for her kind, down-to-earth and approachable manner.
"She was an exemplary role model and mentor to less experienced staff and a strong advocate for changes aimed at improving outcome for critically ill children.
"The support she gave to patients' families was immense and she had a natural ability to put their minds at ease in troubling times.
"Helen was also a wonderful friend and colleague to us all.
"It is typical of Helen that she found time to help children in developing countries through the Chain of Hope charity, travelling as part of a heart surgery team, most recently to Mozambique.
"She will be sorely missed by all of us."
Maureen Betts, head of nursing, child health, at North Bristol NHS Trust, said:
"Susan Andrews had worked within the paediatric critical care team at Frenchay Hospital since February.
"In that short period of time she had become a most liked and respected member of the team.
"She was always very motivated and excelled in her commitment to the children and families and colleagues.
"Her death is not only a great loss to the team at North Bristol NHS Trust but to paediatric nursing.
"Our thoughts are with her friends and family at this time."