At least 44 people died when the passenger ferry sank between two islands in Lake Victoria on Thursday.
Images from the scene showed rescuers in boats alongside the overturned ferry, picking up survivors in orange life rings. The rescuers were also retrieving bodies from the water.
Only 37 people were rescued from the water before poor visibility halted operations.
Regional Commissioner John Mongella told local Tanzania television channel ITV that emergency teams would continue their search Friday morning.
The exact number of passengers on board the boat is unknown, but it may have been carrying 400 to 500 passengers, according to local media reports.
Ferries in Tanzania are often overcrowded, and the lack of an accurate passenger manifest is complicating rescue operations.
Lake Victoria is the largest lake in Africa, which straddles the borders of Tanzania, Uganda and Kenya.
This latest incident underlines the issue of dangerous overcrowding on ferries in the region.
Some 200 people were killed after an overloaded vessel — carrying more than 1,000 passengers despite an official capacity of only 620 — hit strong winds off the island of Zanzibar in the Indian Ocean in 2011.