Prison authorities in Brazil say more than twenty people have been killed in a battle between rival gangs of prisoners in a maximum security jail in the north-east.

They say hundreds of inmates fought each other with home-made knives and clubs.

A BBC correspondent in Brazil says police arrived at the prison, on an island near the city of Recife, shortly after the fighting began, but some reports suggest they did nothing to stop it.

She says the clash probably involved a struggle for control of the drug trade within the overcrowded prison.

Built for four-hundred people, it now houses more than a thousand.