At least 116 people are now known to have died in a fight between rival gangs in Ecuador's jail, officials say, making it the worst prison violence in the country's history.
At least five inmates were decapitated in Tuesday's clashes in the city of Guayaquil, while others were shot dead.
Police commander Fausto Buenaño says the prisoners also threw grenades.
It took 400 police officers to regain control of the jail, which houses inmates linked to global drug gangs.
Local media report that the uprising was ordered by powerful Mexican drug trafficking gangs that are now operating in Ecuador.
Ecuador's prisons service director Bolivar Garzon told local radio the situation was "terrible".
"Yesterday, police took control at 1400 [local time], but last night there were other shootings, other things, explosions and today in the morning we took total control, we are entering the pavilions where there was conflict and discovering more bodies," he said.
It is the latest in a series of deadly incidents involving rival gang members fighting for control of prisons. In February, 79 prisoners were killed in simultaneous fights.
The Litoral Penitentiary, where the latest deadly fight took place on Tuesday night, is considered one of the most dangerous in the country.
Mr Buenaño said that inmates from one wing of the prison had crawled through a hole to gain access to a different wing, where they attacked rival gang members.
More than 80 inmates were injured.
Police managed to reach six cooks who had been trapped in the wing where the fight unfolded and get them to safety.
President Guillermo Lasso has declared a state of emergency in the country's prison system.
The Litoral Penitentiary holds inmates from Los Choneros, an Ecuadorean gang which is thought to have links with Mexico's powerful Sinaloa drugs cartel.
But another Mexican criminal group, the Jalisco New Generation cartel (CJNG), is also trying to forge alliances with Ecuadorean gangs to seize control of drug smuggling routes leading from Ecuador to Central America from its Sinaloa rivals.
In July, President Lasso said that Ecuador's prison system was 30% over capacity.
He announced plans to expedite the process of releasing those inmates who had served most of their time or had committed minor crimes in order to ease the overcrowding.
Source: BBC