Green Day frontman Billie Joe Armstrong has reportedly been discharged from hospital after scrapping a show in Italy on Sunday night due to illness.

The rocker was admitted to the Hospital Maggiore in Bologna suffering a mystery ailment and the band was forced to axed a planned show in the city on Sunday.

No official details about his condition have been released, but local reports suggest the star was suffering gastric problems and discharged himself from the hospital on Monday.

Italian publication La Voce also reports some fans caused problems at the hospital by attempting to visit Armstrong.

The singer's bandmates, Mike Dirnt and Tre Cool, released a video message apologising to fans for the cancellation and promising to be "back as soon as we can."