At least 45 passengers on a bus from Hyderabad to Bangalore were burned to death after the vehicle's fuel tank exploded, Indian officials told Agence France-Presse.
The private Volvo passenger bus was carry 51 people, including two crew members, when it hit a highway divider while overtaking a car. The impact ignited the fuel tank, police believe.
"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," L. Sarman, a senior district administrative official, told AFP.
The driver, a bus cleaner and five passengers managed to climb through a front window of the bus to escape the fire, which burned the bodies inside beyond recognition. Only three of the 45 victims could be identified.
"Authorities are gathering the DNA samples from the bodies" to use in identifying the others, said State Information Minister DK Aruna.
At least five of the passengers were software engineers travelling home to celebrate the Hindu festival of Diwali, The Times of India reported.
According to local police official Pradeep, the sleeper bus had an automatic locking system that could be controlled by the driver.
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Police say that the flames likely started in the front of the bus as passengers had rushed to the rear after the crash. The fire and smoke would have cut oxygen to the back of the bus.
One passenger who managed to escape later died of smoke inhalation.
Prime Minister Manmohan Singh expressed his condolences in an official statement on Wednesday to the families of the victims.
Indian celebrities have also offered their sympathies to the victims and their families.