A passenger bus travelling on a highway in Hungary early on Sunday went off the road and into a ditch where it overturned, killing 12 and injuring others, police said.

The bus, which was carrying a group of Polish tourists, was travelling on eastbound lanes near the town of Mezokeresztes when it overturned on the M3 motorway around 140km (87 miles) east of Hungary’s capital, Budapest, at around 1am on Sunday.

In a statement, police said it was likely that the driver fell asleep, causing the accident, and that the driver had been taken into custody.

Hungary’s National Directorate for Disaster Management said in a statement that 57 passengers and two drivers were travelling on the bus at the time of the accident, and that several of the passengers had been trapped under the vehicle when it overturned.

Polish Foreign Ministry spokesman Maciej Wewior told Polish news agency PAP on Sunday that all of the people on the bus were Polish citizens.

The bus was carrying people from Poland’s southeastern Podkarpackie region who were returning from a pilgrimage in Bosnia-Herzegovina, the regional government in Rzeszow, Poland, said in a Facebook post.