The Yangon to Mandalay bus, which was carrying 27 passengers, hit a traffic island after its tyre burst and then "plunged headlong" into the side of a bridge yesterday, according to the state-run Myanmar language newspaper Myanma Ahlin.
A monk, four men and five women died at the scene in central Bago region, while an 18-year-old male died of his injuries later in hospital.
The report also said a United States citizen in his 30s was among the injured, adding he had been taken to a hospital in Yangon.
Road traffic accidents are common in Myanmar, whose transport network is in poor condition owing to decades of underinvestment by the junta which ruled the country for almost half a century until early 2011.
Earlier this month an editorial entitled "Road slaughter" in the English language state-run newspaper, the New Light of Myanmar, said the country was seeing more road accidents than ever before as vehicles flood into the nation.
It said in April alone, 389 road users were killed in 1346 traffic incidents, with Myanmar police figures suggesting Yangon and Mandalay were the worst affected.