South Africa's animal rights body is probing the death of a giraffe that was reportedly injured as it was being transported on a motorway.

Eyewitnesses say the giraffe, one of two on a truck, hit its head on a bridge on Johannesburg's N1 motorway.

The vehicle then broke down and had to wait several hours to be repaired.

Both animals were then taken to a vet, but the National Society for the Prevention of Cruelty to Animal (NSPCA) said one died on arrival.

The incident has created a stir on the social networking site Twitter.

Thinus Botha tweeted that he had been driving behind the truck when the animal struck its head on Garsfontein Bridge.

There was "lots of blood", he tweeted.

NSPCA's manager Rick Allen confirmed that the giraffe had sustained a head injury but said that an autopsy was necessary to determine the cause of death.

He said the animals were on route to a game farm in Warmbarths, about 160km (99 miles) outside Johannesburg.