The tragedy also injured 37 persons, according to a statement released by the presidency on Saturday.
The tragedy happened near Melela Kibaoni, around 200 kilometres (120 miles) west of the coastal city and commercial hub Dar-es-Salaam, according to Fortunatus Muslim, the police chief of Morogoro’s eastern region.
He claimed the truck swerved out of its lane to pass a motorcycle.
“A truck driver was overtaking a motorbike on his way from the Dar-es-Salaam port to the Democratic Republic of Congo when the two vehicles collided head-on,” he claimed.
The bus was travelling in the other direction from the western city of Mbeya to the coastal city of Tanga, he added.
President Samia Suluhu Hassan presented her condolences on Twitter, and urged “road users to adhere to traffic rules”.
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.
Two years earlier, 42 people were killed in a collision between a coach and a truck.
Still worse was a 2006 accident that saw a 26-seater bus carrying 74 passengers veer off the road near the northern town of Arusha and plunge off a bridge into the river, killing 54 people.