Seven prisoners died and 37 others were wounded in a shootout between inmates at Venezuela's Cabimas Prison, a senior security official said.
"We are dealing with seven deaths and three critically injured who we fear may also die," said Odalys Caldera, the security secretary for Zulia state.
A dispute between two groups of inmates erupted yesterday during visiting hours while inmates' relatives were at the prison, and the incident turned into a violent brawl involving knives and guns.
According to Caldera, the situation is now "totally controlled."
Although Cabimas only has a capacity for 120 inmates, more than 500 are currently held there. Like many Venezuelan prisons, it is plagued by overcrowding and violence.
Last June a violent, month-long uprising at El Rodeo prison near Caracas killed more than 30 people, most of them inmates. It was the bloodiest episode in a Venezuelan prison in the past decade.
And in July, armed clashes between inmates in several Venezuelan facilities left more than a dozen people dead and thirty wounded.
The government has launched a plan to decongest the prisons, which currently house about 50,000 prisoners, though they were only built for 14,000.
During the middle of the El Rodeo crisis the government of leftist President Hugo Chavez created a Ministry of Corrections, whose new head proposed the "conditional" release of nearly half the prison population and a moratorium on sending people to prison. The measures were eventually revoked.
According to humanitarian organisations, about 300 prisoners in the country die each year, and 121 died in the first quarter of 2011.