Country's chief prosecutor and an inmates' rights group said that the blaze engulfed the cells of a police stations Carabobo state after prisoners reportedly set mattresses on fire in an attempt to escape.
"In light of the terrible events that took place in the Carabobo state police headquarters, where 68 people died in a presumed fire, we have appointed four prosecutors... to clarify these dramatic events," chief prosecutor Tarek William Saab said on Twitter.
Carlos Nieto, head of Una Ventana a la Libertad (A Window on Freedom), said that the prisoners in an attempt to break out put mattresses on fire and tried to steal a gun of a guard.
Rafael Lacava, the governor of Carabobo state, expressed dismay over the incident.
"A serious and profound investigation has been initiated to find the causes and those responsible for these regrettable events," he said on Twitter.
Relatives of prisoners gathered outside the jail, demanding information about their loved ones. Police fired tear gas shells on people to disperse them after an officer was injured in stone pelting.
According to Khaleej Times, Venezuela's prisons suffer from dire overcrowding and a shortage of basic supplies, struggling under the deepening economic crisis that is gripping the once-wealthy oil-producing country.
Because of the lack of space in penitentiaries, convicts are often sent to police holding cells like the ones in Carabobo, meant to be used as temporary pens for suspects facing charges or court hearings, where detainees are supposed to spend a maximum of 48 hours.