Patancheru police said the bus, hired by the NGO Help Age India Foundation, was carrying about 40 people when it was hit by a truck from opposite direction while taking U-turn near Isnapur on Hyderabad-Mumbai highway.
The injured persons were shifted to government hospitals at Patancheru, Sangareddy and Hyderabad.
The NGO had arranged an excursion for senior citizens in the area. The bus was on its way to Nagarjunasagar when the mishap took place.