Police said the incident occurred early on Wednesday when a temple palanquin, or temple car, came in contact with a high-voltage line at Appar Swami temple in Kalimedu in Thanjavur district.
Hundreds of devotees were part of the religious procession at the time of the accident.
More than a dozen people were riding the chariot when it came into contact with an overhead high-voltage power line.
Three people are in serious condition with severe burn injuries, police said.
Television footage showed the aftermath of the accident, with the palanquin completely scorched from the incident.
“Eleven people have been killed and 16 people are injured … the palanquin came into contact with high tension wire at 3am last night. The people have burn injuries,” Dinesh Ponraj Oliver, district collector, told The National.
Police said that while the power lines along the procession route are turned off to avoid any untoward incident, the palanquin height was not enough and the power supply was not stopped this time.
The chariot was heavily decorated with flowers and lights and was connected with a power generator electricity supply, increasing the height of the chariot to 2.7 metres.
The structure lost balance while doing a U-turn and touched the live wires, causing fire.
“A case has been registered and investigation is underway,” said V Balakrishnan, a police officer in Tiruchirappalli.
Chariot processions are a common practice in many Indian festivals, particularly in southern India, where temple deities are seated in a chariot and taken out on a procession.
Hundreds of devotees pull the chariots, usually decorated with flowers.
Prime Minister Narendra Modi called the incident “deeply painful” and wished for the speedy recovery of those injured.
“Deeply pained by the mishap in Thanjavur, Tamil Nadu. My thoughts are with the bereaved families in this hour of grief. I hope those injured recover soon,” Mr Modi's office tweeted.
The state chief minister M K Stalin has announced a compensation of 500,000 rupees ($6,500) to the bereaved families of those killed in the incident.