In South Africa, where the buffaloes roam is sometimes a problem

Two buffaloes were spotted walking down the middle of a major highway on Saturday night on the outskirts of the country's biggest city, Johannesburg, as cars and trucks whizzed past. Some startled motorists took pictures and videos on their phones.

It's not clear where the buffaloes came from, and no one has reported missing any.

City authorities have decided they need to be caught and moved as soon as possible because of the danger presented by the sharp-horned bovines, which can each weigh up to 800 kilograms (1,760 pounds) and are notorious as fairly grumpy and unpredictable.

The buffaloes disappeared soon after their highway stroll, but security and risk assessment company Bidvest Protea Coin helped authorities hunt them down with a helicopter armed with an infrared camera.

Their body heat was picked up by the camera and gave them away. The chopper spotted them early Tuesday in a bushy area off a highway near Johannesburg's OR Tambo International Airport, said Waal de Waal, chief operating officer at Bidvest Protea Coin.

The helicopter, normally used for responding to crime and tracking stolen cash-in-transit vans, will be used to dart the buffaloes with a tranquilizer gun from the air, de Waal said.

Veterinarian Cliff Bull will do the darting. He said finding them is hard enough but moving buffaloes is the biggest operation.

Because of the uneven terrain and thick bush, Bull said carrying the buffaloes out on a kind of stretcher once they were tranquilized would be extremely difficult. So, the best bet is to dart them with a mild tranquilizer that allows a team to guide the drowsy animals to a truck with cattle prods.

"We're probably going to have to walk them out," Bull said.

Herding buffaloes tests the mettle of the bravest vets, he said.

The buffaloes might have been on the loose for months after reports of other sightings in the region last April.

Surprisingly for big animals, "they have got a way of getting around without being seen," Bull said.

This is not the first wild animal operation undertaken by Bull, who runs the Craig View Veterinary Clinic in Johannesburg.

He once darted and removed a leopard that someone discovered in the laundry room of their house in the nearby town of Benoni, he said. Bull was also called to remove a bushpig, a kind of wild hog, on the loose in the streets near Johannesburg's high-rise financial district of Sandton.