The MV Nyerere sank Thursday afternoon, just metres from the dock.
Over 40 dead as ferry capsizes in Lake Victoria
More than 40 people died on Thursday when a ferry capsized in the south of Lake Victoria, a Tanzanian government spokesman said.
"According to reports that President John Magufuli has just received from the authorities in Mwanza, the toll now stands at more than 40 dead," Gerson Msigwa, the president's spokesman said on state television.
The boat, the MV Nyerere, sank during the afternoon just a few metres from the dock in the Ukerewe district, national ferry services operator TEMESA said.
The service had yet to establish how many passengers were on board, spokeswoman Theresia Mwami said. State radio said 26 people had been rescued.
Mwami said TEMESA had carried out maintenance on the ferry in recent months, overhauling two engines.
In 1996, a ferry disaster on Lake Victoria in the same region killed at least 500 people.
In 2012, at least 145 people died in a ferry disaster in Tanzania's semi-autonomous archipelago of Zanzibar in the Indian Ocean, on a vessel that was overcrowded.