Relatives waiting for news outside a prison in Venezuela where 68 inmates died in a fire have been tear-gassed by police.

The blaze started when prisoners became embroiled in violence during an attempted breakout at the detention facility in the northern city of Valencia, which is attached to a police station.

Families of the prisoners, who were hoping for news outside the police station, were dispersed with tear gas - while others came up against police officers wielding riot shields.

One woman outside the jail, Dora Blanco, said she was "desperate" to find out what had happened to her son, who was a prisoner at the facility.

She told local media: "I am a desperate mother. My son has been here a week. They have not given any information."

Another mother, Aida Parra, cried: "I don't know if my son is dead or alive. They haven't told me anything."

There are reports that a number of people burned to death during the unrest, and a policeman is recovering in a stable condition after being shot in the leg. Another has been wounded by a thrown stone.

Firefighters have now extinguished the blaze, which reportedly started when inmates set fire to mattresses.

A woman kicks at a riot police shield as relatives of prisoners wait to hear news about their family members imprisoned at a police station where a riot broke out, in Valencia, Venezuela | Image: Juan Carlos Hernandez/AP/Press Association Images

Chief prosecutor Tarek William Saab confirmed the death toll on Twitter, which includes two women thought to have been visiting the cells, adding that four prosecutors had been assigned to "clarify these dramatic events".

It is the latest deadly incident at one of the country's overcrowded jails, with the prison believed to have a capacity of about 60.

Rafael Lacava, the governor of Carabobo state, said: "A serious and profound investigation has been initiated to find the causes and those responsible for these regrettable events."

His local political opponent, Juan Miguel Matheus, has demanded that those waiting outside the facility be informed what had happened, adding: "The desperation of relatives should not be played with."

Many Venezuelan jails are lawless and have been for decades.

The overcrowding at many of the country's penitentiaries means convicts are often sent to temporary pens designed for suspects facing charges and court hearings, where they are only supposed to stay for up to 48 hours.

Two weeks ago, 58 detainees had to be recaptured after escaping holding cells on the popular tourist spot of Margarita Island, and in August 2017 a riot at police cells in the southern state of Amazonas left 37 dead and 14 wounded.

Last April, a dozen people died and 11 were injured when rival gangs fought at the Puente Ayala prison in the eastern city of Barcelona, and a month before that the remains of 14 people were found in a mass grave at the General Penitentiary of Venezuela in San Juan de Los Morros.

Activist Humberto Prado said of the country's prisons: "There are people who are inside those dungeons, and the authorities do not know they exist because they do not dare to enter."