Officials in Brazil say at least 100 juvenile offenders have escaped from a detention centre in the city of Sao Paulo.

The police are using helicopters and police dogs to search for the escapees.

Earlier this week, the international organisation Human Rights Watch criticised Brazil over the abuse of children in its prisons.

The group said children were routinely beaten by police and other youths in detention centres.

It also said the authorities failed to provide the children with medical care and education.

Correspondents say there have been 30 jail breaks and rebellions so far this year in Brazilian prisons.

The Brazilian Justice Minister, Marcio Thomaz Bastos, has called for a complete reform of the country's prison system which he labelled a disaster.

The minister blamed the situation "on failures which had existed for decades" and a relaxation in the enforcement of laws, adding the system was saturated and there were numerous overcrowded prisons.

Mr Bastos comments follow a television broadcast on Sunday which showed inmates in a prison in Rio de Janeiro taking drugs and using mobile phones.

The high levels of overcrowding combined with low levels of staffing mean that the state authorities have in many cases lost control of many areas of the country's prisons, correspondents say.

The inmates dug a tunnel 50 metres long, under two buildings and beneath the boundary wall at Silvio Porto prison.

Officials at the prison, in the town of Joao Pessoa in Paraiba state, said it was the largest breakout in the state's history.

Only three of the 84 who absconded have so far been recaptured.

One man was returned to detention after he was caught mugging a woman on a beach near the prison.

Brazil's jails are notorious for overcrowding, with poor conditions leading to regular escape attempts.

Silvio Porto houses about 700 inmates.

Staying put

The tunnel was one metre wide and the prisoners even equipped it with lighting.

But although the escapees set a new record, there were another 41 who turned down the chance and stayed behind in their cells.

A local prison official admitted that although signs of restlessness had been detected among the inmates recently, their cells had not been searched.

In Rio and Sao Paulo where there are now many members of organised crime gangs in the prisons, escape attempts have also become more sophisticated than the traditional tunnel or shoot-out methods, says the BBC's Jan Rocha.

A few weeks ago a helicopter was hijacked and made to land on the roof of the Sao Paulo prison to rescue three high-ranking members of a criminal gang.

The escape failed when prison guards opened fire.

And last week the director of a Rio prison was shot dead, apparently for trying to introduce stricter rules to improve security.

The authorities in Brazil say a riot in overcrowded police cells on the outskirts of Sao Paulo has left 10 people dead.

Sixty prisoners escaped during the violence at the Embu das Artes jail.

There were 164 prisoners were being held in cells designed for 24 people.

The police say two inmates were killed by other prisoners and eight others suffocated from the fumes of burning matteresses.

The authorities say the riot ended when inmates surrendered.

A BBC correspondent in Brazil says the uprising once again highlights the appalling overcrowding and poor conditions in the country's jails.

Message reads: Peace, justice, freedom

Brazil incarcerates more people than any other country in Latin America.

Its prison system was recently described as a "reinvention of hell" by a congressional commission.

Riots are endemic to the country, where inhuman conditions and over-crowding have been heavily criticised by human rights groups.

Many prisons hold two to five times more inmates than they were designed for.

Carandiru, which has been the focus of the hostage stand-off, holds some 8,000 prisoners, despite being built to accommodate only 3,500.

Packed cells

It is Latin America's largest penitentiary and was the scene of a police massacre of 111 prisoners in 1992.

Authorities had hoped to close the concrete maze in the centre of São Paulo, but a rise in crimes and convictions prevented them from transfering prisoners to less crowded facilities in rural areas.

Overcrowding in many of the country's prisons has reached inhuman levels, according to Human Rights Watch.

It says that in densely packed cells and dormitories, some prisoners are tied to windows to lessen the demand for floor space.

Others are forced to sleep on top of hole-in- the-floor toilets.

Routine torture

The spread of infectious diseases, such as tuberculosis and HIV/Aids, is rife.

Prisoners feel as if they have nothing to lose

Medical care for detainees, including those with terminal illness or severe disability, is generally inadequate or non-existent, human rights groups say.

Prisoners have complained of being routinely beaten and subjected to methods of torture including the "parrot's perch" (suspension by the legs and arms from a metal bar), near- asphyxiation and electric shocks.

The high levels of overcrowding combined with low levels of staffing mean that the state authorities have lost control of many areas of the prisons.

No-go areas

These are in effect run by a small and violent group of inmates.

Human rights groups have long denounced the power of criminal organisations, which have special privileges in the prisons.

A study of the São Paulo region by human rights organisation Amnesty International, revealed fellow prisoners were responsible for more than 80% of deaths of prisoners in custody.

In many large jails the accommodation blocks are no-go areas for prison officers: prisoners with privileges are responsible for locking cells and for notifying prison officers if an inmate is ill and needs attention.

Inmates in the Céu Azul wing of the men's penitentiary in Manaus have complained to Amnesty that the prison administration was using certain inmates to beat and punish others.