Prince Harry and Prince William raced into the South African wilderness on motocross bikes as they began an epic trek in aid of charity.

The physically demanding and mentally gruelling 1,000 mile adventure has been billed as a life changing "endurance test" for the royal brothers by organisers.

It is also the first time William, 26, and Harry, 24, have joined forces to personally raise funds for charity since they staged the successful Concert for Diana last year in memory of their mother. The pair have donated a minimum of £1,500 to take part in the Enduro Africa 08 event that has raised more than £300,000 for three organisations working in southern Africa.

Harry's charity Sentebale, established to help disadvantaged children in Lesotho, especially Aids orphans, will benefit along with Unicef and the Nelson Mandela Children's Fund - both working in South Africa to either help communities blighted by Aids or improve the prospects of youngsters.

Simon Smith, organiser of the event, said: "This is not a race it's an endurance test, it's all about finishing the route. It will grow you as a person by taking part. Most days will be spent on goat tracks with wonderful tribal people who see the world in a very different way to us.

"The riders will face 60-degree ascents which will be a great challenge. Much of it will be down to mental fitness. The Princes have bags of personality and are big characters - they are both in the forces and it shows. Mike Glover, our logistics director, will lead William and Harry's group and he's like a Sergeant Major, a real force of nature. If you don't think you can do something he still will, and you will do it."

The Princes are amongst more than 80 riders taking part in the eight-day cross-country motorbike trek that began with the deafening sound of dozens of bikers speeding away from the holiday resort of Port Edward, on Kwazulu Natal's southern coast.

The Princes were dressed for the potentially dangerous bike ride in crash helmets, goggles, light body armour and protective boots like everyone else. They will travel in a group of around ten across the South African terrain and all the fundraisers will meet up at the end of each day to nurse bruises and share stories before reaching the final stop of Port Elizabeth.

William said: "The main reason why we're doing it is Harry and I had an idea last November to take part in this rally because it's a mixture of adventure and charity. The key being the money raised today goes towards Nelson Mandela's Children Fund, Unicef and Sentebale - three absolutely brilliant charities."

Harper Brown, Sentebale's country director, said Harry became involved in the motorbike adventure after Enduro Africa approached his organisation and offered to raise funds for it for three years until 2010. He said: "This funding is vital. Sentebale has a long term commitment to organisations. We not only provide help to children, we provide management support, training and direct funding into those organisations. And we are one of the few charities who pay for salaries and running costs so our ongoing commitment needs funding."