The crash happened near Zibo in Shandong province when a bus collided with a car, the state-run Xinhua news agency reported.
The bus lost control and smashed through a median barrier into the path of the second bus, which flipped into a ditch, police said.
Police spokesman Wang Jiguo said six people were declared dead at the scene. Another seven people died in area hospitals, he said.
There wasn't an immediate cause known for what sparked the collisions, the report said.