The accident also injured 38 people, the presidency said in a statement on Saturday, AlJazeera reported.
The police chief of the eastern region of Morogoro, Fortunatus Muslim, said the accident occurred in Melela Kibaoni, some 200km (120 miles) west of the coastal city and economic hub Dar-es-Salaam.
He said the truck left its lane to overtake a motorbike.
“The truck driver, who was heading from the Dar-es-Salaam port to the Democratic Republic of Congo, was overtaking a motorbike when the two vehicles collided head-on,” he said.
The bus was travelling in the other direction – from the western city of Mbeya to the coastal city of Tanga, he added.
Tanzania has seen a spate of fatal traffic accidents.
On Monday, four people were killed in a coach accident outside the southwestern town of Tunduma, near the Zambian border, on its way to Dar-es-Salaam.
In May 2017, 35 people – 32 of them schoolchildren – were killed in a bus crash. The vehicle had been speeding.