State-run agencies have bought 11.92m tonnes of wheat from farmers so far this season, down 25% on the 15.92m tonnes bought in the same period a year ago
The road crash also injured another 13 people aboard the bus that was travelling from garrison city of Rawalpindi to Quetta, the capital of southwestern Balochistan province, said Ijaz Jaffar, deputy commissioner of Sherani district.
The ravine is some 350 kilometres north of Quetta.
Poor road infrastructure and rash driving often cause deadly road crashes in Pakistan.
The province is home to several Chinese projects under an investment plan in which Beijing is seeking road and sea trade linkages with the world.