Reports on the ground indicate that at least 31 people drowned and 123 others were still missing.
Seven children were among the dead as preliminary information indicated there were a total of 290 people on board, including nine crew members and 31 children, when the ill-fated ferry MV Skagit capsized in the Indian Ocean Wednesday afternoon.
The ferry was heading to Zanzibar from the capital of Dar es Salaam when it sank near Chumbe, a coral park and former army base, about 10km from Unguja, Zanzibar's main island.
Strong winds and high waves were blamed for the tragedy, which according to the survivors, led to engine failure and consequent tilting and sinking of the vessel.
In a statement, President Jacob Zuma expressed his support to Tanzania for their continued efforts to rescue the survivors.
He also indicated South Africa's readiness to assist where possible.