Nine persons were injured when a 'petrol' bomb exploded inside a private bus near Perambur, police said on Friday.
The explosion occurred when the bus carrying about 45 passengers reached Eechampatti on Thursday evening.
Police said four passengers, who were travelling on the foot board, and five passengers inside the bus were injured in the explosion.
The injured had been admitted to Ammapalayam Government Hospital.
The bus was plying from Perambalur to Turaiyur.
Police said some persons were being questioned regarding the explosion.