Around 400 buffaloes drowned after stampeding into the Chobe River along the border between Botswana and Namibia, possibly while running away from lions, the tourism ministry said.

The Chobe River flows along the northeastern border of the Chobe National Park, known for the large breeding herds of elephants, giraffe, sable and African buffalo, which make it a major tourist attraction in Southern Africa.

Initial investigations Botswana and Namibia suggest that an exceptionally large buffalo herd was grazing in Namibia before they stampeded into the Chobe River. The buffalo trampled on each other and fell into the river from its steep banks, the ministry said in a statement.

"The cause of the stampede is still uncertain and under investigation. However, initial indications are that they were being chased by a pride of lions," Botswana's Ministry of Environment, Natural Resources Conservation and Tourism said.

"This is not an unusual occurrence as mass drownings have occurred before in the Chobe River notably off Sedudu Island."