Deodatus Kinawilo, district commissioner for Bukoba, the town close to the epicentre of the quake, said 14 people had been confirmed dead following the quake that struck early afternoon on Saturday.
The previous toll from local authorities was 13 dead and 203 injured.
A group of 15 boys who were secondary-school boarders in the worst-hit city of Bukoba, which is in Kagera province bordering Uganda and Rwanda, were believed to be among the casualties.
Prime Minister Kassim Majaliwa is to join mourners at the Bukoba stadium later Sunday.
The city suffered widespread damage, with 270 houses demolished and electricity disrupted, the Red Cross said in a statement.
Bukoba's main hospital was stretched to nearly full capacity and had limited stocks of medicine, the Red Cross said.
"Telecommunications have been disrupted and we are trying to get a clear picture of the damage to hospitals and other essential infrastructure," Andreas Sandin, Red Cross operations coordinator in East Africa and the Indian Ocean Islands, said in a statement.
Significant shaking was also felt in parts of nearby Uganda, western Kenya and Rwanda.
"So far, no further damages have been reported in Kenya, and minor damages reported in Uganda," the Red Cross said.
