The ferry is believed to have been carrying a total of 200 passengers which is double the ferry’s capacity when it capsized close to the pier at Ukara Island on Thursday afternoon, according to state media.
However, Tanzania’s Electrical, Mechanical and Services Agency, which is responsible for ferry services, said it was unknown how many passengers were aboard the MV Nyerere.
The ageing ferry was also carrying cargo, including sacks of maize, bananas and cement, when it overturned and then sank around 50 metres (55 yards) from Ukara dock.
The cause of the accident was not immediately clear, but overloading is frequently to blame for such disasters.