Inmates armed with homemade knives fought each other for about seven hours over territory and money, leaving seven dead in the worst US prison riot in quarter of a century, officials said.

Police and specialist guards have been called to a prison following reports of a riot involving up to 200 inmates.

A prison riot in north-eastern Brazil left at least seven dead after a fight between two gangs escalated and led to about 70 people, many visiting family members, being held hostage for several hours.