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.
From the newsroom of the BBC World Service