Two brothers are in a serious condition after being attacked by a black rhino while on a game hike in northern KwaZulu-Natal.

Mark Crozier, who turned 34 on Wednesday, and his brother Sean, 36, were on the second day of a hike in Hluhluwe-Umfolozi Park when they and a group of foreign tourists were charged by the rhino.

Crozier, a writer for a Bahrain magazine, had decided to celebrate his birthday by going on a game adventure.

Witnesses said the group were four hours from the Impila camp on the second leg of the hike when the rhino came charging at them from a river.

Two game rangers fired warning shots at the rhino, while the tourists tried to hide in dense bush.

The rhino, however, continued its charge, throwing Mark and Sean over its back and seriously injuring them.

Speaking from her Durban home, Mark and Sean's mother, Dawn, said she had heard that after attacking Sean, the rhino turned on Mark again.

It gored and crushed him into the ground with its horn before trying to flee.

"As the rhino fled, the game rangers shot it dead," she said.