The incident at the prison in the town of Irribarren, which erupted on Thursday, came just days before socialist President Nicolas Maduro seeks re-election to a second term in the crisis-hit South American country.
"There was an uprising resulting in 11 deaths, including two guards and nine prisoners," Carlos Nieto, the director of prisoners' rights group A Window on Freedom, told AFP.
Inmates snatched a gun from a guard, sparking a 20-minute shootout, the group said, quoting family members of the victims.
The dead and wounded were apparently either shot or stabbed.
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.
Nearly 400 people have died in the country's prisons since 2011, according to official figures and rights groups.
In March, 68 people died in a fire in a police station's jail in the northern city of Valencia. The blaze was started by detainees who wanted to force the guards to unlock the cells in a bid to escape.
Last month, five police officials were charged with homicide over the fire, one of the deadliest in Venezuela's long history of prison disasters and which triggered national outrage and UN condemnation.
A Window on Freedom has blamed the government for overcrowding at provisional detention centers, where prisoners are not supposed to spend more than 24 hours but can remain many months awaiting trial.
The group estimates the prison system to be 400 percent overpopulated.
Maduro is seeking a second six-year term in a controversial election on Sunday that is being boycotted by the opposition.
Maduro is the clear favorite, despite trailing in opinion polls to his main rival Henri Falcon, and a low approval rating among Venezuelans fed up with hyperinflation, food and medicine shortages, rising crime and broken water, power and transportation networks.
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