The double decker bus from Denmark was between the towns of Dessau and Wolfen on the A9 motorway when it hit the central dividing barrier and flipped over around 1am.
The bus was carrying 66 passengers – all of them Danish. A considerable number of children were on board, though the passengers killed were all adults, a police spokeswoman said.
The bus driver was among the seriously injured. The exact number of injured was unknown and investigations into the cause of the crash were continuing. There were initial suggestions at the scene that the bus was passing or overtaking other traffic when the accident happened but this was not confirmed.
The motorway was still closed in both directions late Saturday morning as emergency crews continued their work at the scene. One person was still trapped in the wreckage, police said.