Picture used for illustrative purposes only.
The New Delhi Television channel said the truck, crowded with devotees, also caught fire due to the electric spark.
Another three people suffered burn injuries and were hospitalised in Thanjavur, a city in Tamil Nadu state, a police officer said on condition of anonymity because he was not authorised to talk to reporters.
The deaths occurred early on Wednesday when the temple chariot procession was under way in Thanjavur district, 340 kilometres (210 miles) south of Chennai, the state capital, police said. The procession was organised by a local Hindu temple. Other details were not immediately available.
Thanjavur is an important centre of South Indian religion, art, and architecture. The area is known for its heritage temples.