"Without warning or provocation it launched itself into the safari truck and grabbed the ranger's arm. Fortunately he had a bush jacket on.
"What followed was insane. The occupants of the safari truck were screaming.
"Some of the people seated behind the ranger tried to help by beating the animal with their cameras."
Witnesses said the occupants of a Hyundai minivan travelling ahead then hit the leopard with their car door. But it still did not release its grip on the guide.
Mr Plumb was able to reverse the vehicle and free himself from the leopard's grip - but even that was not the end of the ordeal.
Mr Ford said: "The leopard charged after the vehicle and hunted it down.
"It leapt onto the bonnet of the vehicle in an apparent attempt to get to the occupants. The ranger then braked and the animal fell to the ground.
"Again it launched itself at the vehicle. The ranger was left with no alternative than to take it out. He drove over the animal's hind legs. It got up clearly injured.
"The minivan then also went at it and drove over the leopard."
Mr Plumb, who has been working as a guide for four years after moving to South Africa from the UK, was taken to hospital for immediate surgery. He is said to be in a stable condition.
William Mambasa, general manager at Kruger National Park said: "We would like to thank the tourist from another vehicle for his quick and decisive action as he saved the guide and tourists' lives.
"It is suspected that the leopard was fighting with another one as its hind was badly injured - the other leopard was spotted in the area watching from a distance."
In a statement, South Africa National Parks said Mr Plumb is a field guide working for a private open safari vehicle company at Kruger National Park.
The leopard was put down after the incident, which comes just a month after a lion mauled 22-year-old American tourist Katherine Chappell to death in a predator park in South Africa.
