At least seven people have been killed in a shooting at a prison near the Guatemalan capital Guatemala City.
Some 1,500 soldiers and police officers were reportedly sent to the prison to try and stop the violence.
Another 20 people were injured in the gunfire, and have been taken to hospital for treatment.
Officials say the incident was sparked by a fight between two inmates, one of whom was "in an alleged state of intoxication".
Pavón prison houses at least 4,000 inmates, despite originally being built for only 1,000 people in the 1970s.
Inmates had control of the prison for about eight hours on Tuesday, officials told the Associated Press news agency.
"Security forces have already entered and have regained control of the centre," Carlos Morales, a spokesman for Guatemala's prison system, later told Reuters news agency.
He also told local media that the shooting started with "a confrontation between an inmate in an alleged state of intoxication, shooting at another inmate".
In 2016, 14 people were killed in a riot that broke out in the same prison.