The bus caught fire shortly after 5 am when most of the passengers were asleep
It was a little after 5 am when the bus headed to Hyderabad from Bangalore hit a barrier on the highway. The passengers on board were sleeping when the Volvo went up in flames. 45 people were killed, many of them burnt alive.
Five passengers and the driver and cleaner of the luxury bus managed to escape the inferno.
The driver has reportedly told the police that he was trying to over-take another vehicle when he hit a divider. The fuel tank then exploded, say investigators based on early inquiries.
"The driver was speeding at about 120-130 kilometres (75-80 miles) an hour. He was driving all night, it seems he may have fallen asleep at the wheel," said L Sarman, a senior district official to news agency AFP.
Among those who were killed were five employees of IT giants like IBM and Google, headed home to Hyderabad for Diwali.
The bus belonged to Jabbar Travels, a well-known tour operator, with offices in Bangalore, Hyderabad, Mumbai and Pune. "The driver was not over-worked or new," said Imtiaz Khan, a manager. Relatives of the victims screamed and broke down in tears outside the office of the vehicle operator in Hyderabad, 140 kilometres from the crash site.
The bus had just one door in the front. The police say say that a large glass window meant to serve as an emergency exit could not be broken because a hammer, meant to be placed near it, was missing.