A wild bear spotted by border guards crossing into Hungary from Serbia on Tuesday probably travelled hundreds of kilometres in search of food, an expert said.

The flat Hungarian plain is not a natural habitat for bears, but the animal could have walked a long distance to get there, wildlife expert Balint Kuli told the Index.hu internet portal.

"If a bear has not stored enough fat reserves to survive the winter hibernation, it can go out in search for food," Kuli said.

Hungarian police said border guards at Hercegszanto on the frontier with Serbia saw an unusually shaped animal on an infrared camera late at night.

"A jeep patrol sent to investigate determined the animal, larger than a deer, was in fact a bear," a police statement said.

The animal then took fright and ran back across the border.

Serbian authorities reported that no bears had escaped from a nearby zoo, police said.

Wild bears are still found in forested and hilly parts of Europe, including the Balkan peninsula, but the case is the first in flat southern Hungary, according to Index.hu, a popular Hungarian-language site.