Globo reported that a hooded group attacked supporters near the Fifa Fan Fest in the downtown district of Anhangabaú Valley on Thursday afternoon.
According to reports, a firecracker was thrown at the English contingent before Military Police intervened. Fifteen people were arrested after the melee.
The majority of England fans have been enjoying the build-up to the Uruguay game
Military police said: "A bomb was thrown against England fans who were at the Guanabara Bar and Fruit Planet snack bar."
One eye-witness said: "The guys jumped on a bus to try to escape, and then the police went after them."
Afterwards the attack police seized six rockets, a knuckle-duster, a dagger and other fireworks.
The British Consulate are aware of an incident, but said they are not aware of any casualties.
A statement read: "We are aware of an incident affecting fans around the area of the Fan Festival in São Paulo.
"We are working with the local authorities to establish the facts. No British nationals are believed to have been injured."