Clashes between inmates killed 15 people at a jail in Amazonas state in northern Brazil on Sunday, the regional prison authority said. The clashes broke out around 11:00 am (1500 GMT) during visiting hours at the facility, located some 28 kilometers (17 miles) from the state capital Manaus. "It was a fight between the inmates. There had never been deaths during the visits," Colonel Marcos Vinicius Almeida told a news conference. An investigation has been opened to determine the cause of the fight, Almeida said. Almeida emphasized that authorities had reacted within minutes to the Sunday violence, preventing a potentially worse result. In January 2017, the same facility was the scene of a prison rebellion that lasted almost 20 hours and left 56 people dead. Brazil has the world`s third-largest prison population, with 726,712 inmates as of June 2016, according to official statistics. The population is double the capacity of the nation`s prisons, which in 2016 was estimated to be 368,049 inmates. Along with severe overcrowding, Brazil`s prisons are plagued by gang violence, while riots and breakout attempts are not uncommon.