Twelve people were killed and dozens more were injured when a bus transporting Catholic pilgrims back to Poland veered off a Hungarian motorway early Sunday.

Police said the bus overturned after coming off the M3 motorway, which connects Hungary’s capital Budapest with the northeastern city of Nyíregyháza, at around 1:00 a.m. Sunday. Officers have reported that the driver may have fallen asleep at the wheel.

The tour group was returning from Medjugorje in Bosnia and Herzegovina, a popular pilgrimage site for Catholics where multiple visions of the Virgin Mary have been reported.