About 200 prisoners are said to have been in the current prison ward when the riot broke out at 02:00, local time, on Tuesday night in the Colombian city of Tuluá.
After that, a fire must have broken out.
According to Reuters, it is not yet clear what caused the riot.
But according to information to El Tiempo, the unrest must have started in connection with an escape attempt.
A total of 49 prisoners are said to have died and at least 30 were injured.
None of the dead should be guards, local authorities say.
According to El Tiempo, the events are reminiscent of the protests in the La Modelo prison in Bogotá 2020, when 24 inmates died during protests demanding corona measures.