The early morning crash occurred near the southern village of Modriach when the bus, with 42 people aboard, veered off a highway lane and onto a guide rail, police said in a statement. The bus came to a standstill tilted on its right side after sliding some 50 meters (164 yards.)
Hungarian Foreign Ministry spokesman Lajos Szelestey said the bus was one of two bringing soccer fans back to Hungary from Milan, Italy, following Sunday's match between AC Milan and Roma. Szelestey said two women and a man died in the crash.
The injured including four in serious condition were taken to area hospitals, police said.
The Hungarian soccer federation said a minute's silence would be held at all soccer matches played in Hungary this week in tribute to the soccer fans who died in the accident.
It was not immediately clear what caused the crash.