A Polish tourist bus crashed into a ditch on a Hungarian highway early Sunday, killing 12 people and injuring 10 others, including five critically.

The bus was carrying 57 passengers and two drivers and was reportedly transporting pilgrims from Serbia back to Poland.

Eleven people died at the scene, while another died in a hospital, and dozens of others were treated for minor injuries.

The driver was detained, with police reportedly saying he may have fallen asleep at the wheel before the crash near Mezokeresztes, Euro News has reported.

Poland sent medical and consular assistance to Hungary, while officials offered condolences as authorities investigated the country’s deadliest road accident in more than two decades.