The engineers, who worked for IBM and other software companies, were travelling to Hyderabad to celebrate the festival of Diwali with their families, The Times of India reported.
NDTV television channel, quoting police, said the vehicle's fuel tank caught fire after striking the railing when the driver attempted to overtake another vehicle. The fire engulfed the entire vehicle.
A few passengers escaped by breaking windows in the bus.
The other passengers could not get out of the vehicle because its central locking system made it impossible for them to open the door or the emergency windows, said district collector M. Girija Shankar.
The crash occurred near Mahabubnagar district in southern Andhra Pradesh state as the bus traveled from Bangalore to Hyderabad, capital of Andhra Pradesh.
Most of the passengers were asleep at the time of the crash.
The report quoted police as saying there were 49 people aboard the bus.
The Press Trust of India, quoting police and witnesses, said the bus driver and his helper were among those who escaped the blaze.
"It seems the bus was travelling at a high speed when its fuel tank hit the roadside culvert and caught fire," a senior police official said.