The incident happened when a roadways bus collided with a private bus on Gorakhpur-Deoria road near Motiram Adda, they said.
Chief Medical Superintendent of the district hospital H R Yadav said that 15 persons were injured in the accident out of which four persons who have sustained serious injuries have been referred to Baba Raghavdas medical college.
Police said that those killed in the accident could not be identified so far.