A couple visiting a South African national park captured the moment a pair of heroic hippos came to the rescue of a wildebeest that was being attacked by a crocodile.

A video posted to YouTube on Tuesday by Kruger Sightings shows the wildebeest in Kruger National Park struggling to escape from the crocodile, which has its jaws clamped down on one of the creature's legs.

The croc works for several minutes to drag the wildebeest into the water as it struggles in vain to escape from the predator's powerful jaws.

The wildebeest is showing clear signs of exhaustion and appears to be done for when a pair of curious hippopotamuses swim up and start observing the situation.

The hippos suddenly rush the croc, causing it to drop its grip on the wildebeest's leg and allowing the would-be meal to escape.

Mervyn Van Wyk, 72, captured the video Friday morning while driving with his wife close to Transport dam, near Skukuza inside the park.

"We could not believe the rarity of this situation. I have never seen a hippo coming to the aid of another animal, it was simply astonishing. Remember in Kruger, never rush away and always be patient because these amazing sightings are everywhere to be seen," Van Wyk said.

Experts suggested the hippos may not have been actually attempting to help the wildebeest, but rather putting on a territorial show to chase the invading animals out of their turf.