Officials say a bomb has exploded outside a maximum security penitentiary in southeastern Brazil and opened a hole in one of the prison walls.

The Sao Paulo State Prison Affairs Department says in a statement that none of the prison's inmates escaped and that no one was hurt by the Friday morning blast at the Adriano Marrey Penitentiary on the outskirts of the city of Sao Paulo.

Police say that two men hurled "an explosive device" that opened a "large" hole in the prison wall. They fled on foot.

Further details were not immediately available.