"There are people who are inside those dungeons ... and the authorities do not know they exist because they do not dare to enter," said Humberto Prado, a prisons rights activist.

Aida Parra, who said she last saw her son a day before when she went to deliver him food, said, "I don't know if my son is dead or alive!"

"They haven't told me anything."

A Window to Freedom, a nonprofit group that monitors conditions at Venezuela's jails, said preliminary but unconfirmed information indicated the riot began when an armed detainee shot an officer in the leg.

Shortly after that a fire broke out, with flames growing quickly as the blaze spread to mattresses in the cells, it said. Rescuers apparently had to break a hole through a wall to free some of the prisoners inside.

Photos shared by the group showed prisoners being taken out on stretchers, their limbs frozen in awkward positions as skin peeled off.

A Window to Freedom's director, Carlos Nieto Palma, said officials should be held accountable for failing to address deteriorating conditions in police station jails. The group said overcrowding has become common throughout the country as detainees are kept long past customary brief holding periods before being sent to other larger jails before trial or freed.

"It's grave and alarming," Nieto Palma said. "What happened today in Carabobo is a sign of that."

Outside the police station, some relatives buried their hands in their faces as tears streamed down their cheeks. Others had to be held up with the support of friends and family as they collapsed in despair. Still others wept quietly and clutched their hands in prayer.

Reuters, AP