The accident occurred just before 2 am (midnight GMT) when a Polish bus crashed into the back of a Ukrainian bus. The Polish bus then broke through the central barrier and collided with a Polish minibus travelling in the other direction.
The first bus then skidded down a slope.
Police said six of the nine dead had been identified. They were Polish citizens. Some of the 43 people injured were severely hurt, police said.
The A4 motorway, which links Germany with Poland via Dresden, was closed for hours in both directions.