DAR ES SALAAM (Reuters) - At least 13 people, 11 of them children, drowned when a boat carrying them back from a trip to a Tanzanian hospital for vaccinations capsized on Lake Tanganyika, the police said on Thursday.

Initial investigations indicated the boat sank when it was hit by strong winds on Wednesday, Rukwa regional police commander Jacob Mwaruanda said. It was unclear how many people had been on board.

"The boat was full of mothers and their children and it sank as they were returning from a hospital at a nearby village where they had gone to take their children for their vaccinations," Mr Mwaruanda said.

The lake, which straddles the border between Tanzania and the Democratic Republic of the Congo, is the world's second largest by volume.