- The ferry sank just a few metres from the dock in Ukerewe district, according to national ferry services operator TEMESA.
At least 136 bodies have been retrieved after a ferry sank on Lake Victoria, Tanzania's top police official Simon Sirro says.
Scores more were still feared missing as rescuers searched for survivors on the morning after the disaster.
Officials are concerned the final death toll could climb to more than 200, with initial estimates showing the MV Nyerere was carrying more than 300 people.
"With God's help, we rescue those who are alive," Mwanza district commissioner John Mongela had said earlier.
Hundreds feared dead in Tanzania ferry accident
He said two other vessels had been diverted to help with the rescue operation.
The ferry sank just a few metres from the dock in Ukerewe district, according to national ferry services operator TEMESA.
But it was hard to establish the precise number of passengers on board since the person dispensing tickets had also drowned and the machine recording the data had been lost.
TEMESA spokeswoman Theresia Mwami said the operator had carried out maintenance on the ferry in recent months, overhauling two engines.
Thirty-seven people had been rescued from the sea, said Jonathan Shana, the regional police commander for the port of Mwanza on the south coast of the lake.
Mr Shana said more rescuers had joined the operation when it resumed at daylight on Friday, although he did not give exact numbers.
Accidents are often reported on the large freshwater lake that is surrounded by Tanzania, Kenya and Uganda.
Some of the deadliest have occurred in Tanzania, where passenger boats are often said to be old and in poor condition.
Hundreds were killed in 1996 when a passenger and cargo ferry sank on Lake Victoria, and in 2011 and 2012 hundreds more drowned off Tanzania's coast near Zanzibar.