Hassan Abbas, the government’s chief spokesman, was quoted by national broadcaster Tanzania Broadcasting Corporation (TBC) as saying the death toll now stood at 136.
According to sources, the ferry, with a capacity of 101 passengers and 25 tonnes of cargo, capsized at around 1:00 p.m. local time Thursday.
Chief Secretary at State House John Kijazi told TBC that President Magufuli has announced a four-day mourning for the victims, starting Friday.
“During the mourning period the national flag will fly at half-mast,” Kijazi said, adding that Magufuli has ordered the detention of all employees at the ferry for questioning.
Magufuli also ordered the arrest of safety inspectors from the country’s transport regulator, the Surface and Marine Transport Regulatory Authority.
Preliminary investigations showed that the state-owned ferry was overloaded and was being manned by someone who was not the authorized captain of the vessel.
Magufuli directed Prime Minister Kassim Majaliwa and Minister for Works, Transport and Communication Isack Kamwelwe to launch full investigations into the sinking.
Majaliwa arrived in Mwanza region on Friday evening and Kamwelwe arrived in the lake region earlier in the day.
There has been a public outrage over the decision of Mwanza regional authorities to call off the search and rescue operation after darkness on Thursday night.
Some opposition leaders called for the resignation of top transport officials over the tragedy.
The last major ferry accident on Lake Victoria occurred in 1996 in the same region, killing at least 500 people.