A biker who hopes to raise £100,000 for Helen House in Oxford by racing 11,000km across two continents has pulled out after suffering serious injuries in the fourth leg of the journey.

Chris Emerson, 47, pictured, was the only amateur out of 400 motorcyclists, four-by-four drivers and truckers to start the dangerous 18-day Dakar Rally on January 1.

Despite suffering broken ribs and cartilage, mild dehydration, a dislocated shoulder, and fluid on the lungs after being thrown from his bike, and battling against Moroccan thieves, he managed to get back on the BMW 650 Rally machine and complete the 752km Tangiers to Er Rachidia stretch.

Despite his early homecoming, he said his sponsorship for the east Oxford children's hospice, was unaffected. Mr Emerson had completed more than 2,000km when he was forced to withdraw on January 4.

Only about one third of contestants complete the Dakar Rally, which starts in Paris and travels through France, Spain, Morocco, Mauritania, Mali, Burkina Faso and Senegal.

On his web-site diary, he said: "I performed aerial acrobatics across the rocks, through the barbed wire fence and down a cliff into the woods.

"Some local kids helped me get the bike upright but unfortunately the water pump housing was cracked and the engine casing had some innovative new aeration. The adrenaline was wearing off and I was really beginning to hurt."

When doctors arrived, Mr Emerson's survival kit had been stolen and although he needed medical attention, he refused to leave until he knew his bike had been safely collected.

As he waited for a recovery vehicle, a trucker helped him patch up the bike and he decided to finish the race.

He said: "There was a group of guys clearing up at the finish and around the spectator car park. They gave me hot tea and their boss used his Mondial Assistance membership to get a rescue truck.

"He put me in his car and lead the truck into Rabat straight to a very nice hotel, and wouldn't take a penny piece as a thank you."