NEW DELHI — At least 48 people were killed and a dozen more injured after an overloaded bus plunged into a gorge in northern India early Sunday, the police said.

The accident occurred in the mountainous state of Uttarakhand, in an area where roads are poorly maintained and often do not have guard rails.

Bus safety is a notorious problem in India, but the toll on Sunday was particularly high even in a country where deadly crashes are all too common, and the situation was worsened by the fact that the crash site was difficult to reach.

Jagat Ram Joshi, the police chief for the district of Pauri Garhwal, where the accident occurred, said it took hours for rescuers to get down the hillside to reach the injured, some of whom were in critical condition. He said it was unclear why the vehicle, which seats 28, had crashed.