DAR ES SALAAM, Tanzania — At least 42 people drowned when a ferry sank in Lake Victoria on Thursday, and Tanzanian government officials fear that the final death toll could be more than 200, a senior local official said.

The official, Col. Lucas Magembe, the Ukerewe district commissioner, told Reuters that the rescue mission to find survivors from the disaster had been halted until dawn on Friday.

Initial estimates showed that the boat, the Nyerere, was carrying more than 300 people.

It sank on Thursday afternoon just a few yards from the dock in the Ukerewe district, according to Tanzania’s Electrical, Mechanical and Services Agency, the national ferry services operator.

It was difficult to establish the precise number of passengers on board, since the person dispensing tickets drowned and the machine recording the data has not been recovered.