The bus, on its way to Tiruppur from Chennai, fell down the bridge as the driver lost control, police said. Some of the bodies of victims were charred beyond recognition.
Out of the 24 onboard in the bus one passenger and the bus driver himself managed to escape. The bus driver, who survived the accident, surrendered to the police.
"There were two lorries ahead of the bus, one lorry hit the other lorry and the bus was just behind them and to avoid collision, the driver took a left turn and lost control, following which the bus fell into a ditch," Vellore DIG Jairaman said.
"Out of the 24 people in the bus, only two managed to come out including the bus driver, the rest were burnt alive," he added.
(With inputs from PTI)