TEHRAN -- Fifty-four people were injured early Sunday after a bus overturned on an intercity road in Iran's central province of Semnan, the official news agency IRNA reported.

The accident occurred on the road from Sorkheh County to the provincial capital Semnan at 4:45 am local time (0115 GMT), Karen Yahyaei, spokesperson for Semnan University of Medical Sciences and Health Services, was quoted as saying.

He added that 10 ambulances and one ambulance bus rushed the injured to a hospital in Semnan.

Commenting on the cause of the incident, Semnan's Traffic Police Chief Mousa Bozorgi said the bus had veered off the road due to the driver's drowsiness, according to the semi-official Mehr news agency.

Investigation was underway to determine the cause of the accident, he said.