The accident occurred during the night of Sunday on the M3 motorway, near the town of Mezőkeresztes.
The Polish-registered bus had 57 passengers and two drivers on board and was en route from Serbia to Poland, police said.
Polish Foreign Minister Radoslaw Sikorski confirms in a post on X that Polish tourists were on board the bus.
In addition to the 12 dead, at least ten people are seriously injured, Hungarian Prime Minister Péter Magyar writes in a statement on social media, in which he expresses his condolences to the victims' relatives.
The accident is the worst road accident in Hungary since 2003, when a German tourist bus collided with a train in Siófok and 33 people died, AFP writes.
