A group of 91 prisoners escaped a jail in northeastern Brazil on Thursday by fleeing through a 30-meter (100-foot) tunnel, Brazilian media said.
Nine of the inmates have been found, while police are attempting to catch the remaining 82 who disappeared from the prison in Parnamirim, in the state of Rio Grande do Norte, according to the Agencia Brasil news agency.
The incident comes just months after 56 inmates escaped from the Alcacuz jail, also in Rio Grande do Norte, during a bloody battle between two rival gangs in which 26 people were massacred.
It was part of an unprecedented wave of violence at the beginning of the year in the country's overcrowded and dilapidated prisons, particularly in the northern region bordering Peru and Colombia, a key route for trafficking cocaine to Europe.
Parnamirim prison was hugely overcrowded, with 589 detainees in a facility designed for 382, according to figures from local judiciary services.
With 622,000 detainees registered by the justice ministry at the end of 2014, Brazil has the world's fourth-largest prison population, behind the United States, China and Russia.
The country's prisons are at 167 percent of capacity.