More than 55 inmates have been found dead over the last two days after violent clashes broke out in separate prisons in northern Brazil.

The majority of the victims were reportedly found in the Antonio Trindade Penal Institute near Manaus, the capital of Amazonas State where the facilities are located.

The Amazonas State Prison agency said the prisoners found dead on Monday all showed signs of asphyxia, adding that the authorities had regained control of the four prisons.

This is even as the Brazilian government said it was sending reinforcements to boost security in the state’s prisons.

Monday’s clashes took place a day after 15 inmates were killed during riots at Manaus’ Anisio Jobim Prison Complex. The clashes broke out about 11:00 am during visiting hours at the facility which is located about 28 kilometres from Manaus.     

In January 2017, the same facility was the scene of a prison rebellion which lasted almost 20 hours and left 56 people dead.

According to official statistics, Brazil has the world’s third-largest prison population, with an estimated 726,712 inmates as of June 2016. This figure is however double the capacity of the nation’s prisons.

Along with severe overcrowding, prisons and detention facilities in Brazil are plagued by gang violence while riots and breakout attempts are not uncommon.