Attacks are continuing in the Brazilian state of Sao Paulo where a wave of co-ordinated violence since Friday has left at least 81 people dead.
Overnight, gangs torched buses, targeted banks and maintained their attacks on police patrols and stations.
At least 23 people were killed in the latest fighting, officials said.
Authorities say the unrest is being directed from inside jail by a criminal gang after hundreds of its members were sent to maximum security prisons.
Correspondents say the violence is an escalation of what many in Sao Paulo are calling a war between the state authorities and the First Command of the Capital (PCC) criminal faction.
Uprisings are said to have been quelled at some 40 jails, but officials are also struggling to restore order in 29. About 120 people are still being held hostage.
Unrest has also been reported in some prisons in neighbouring states, including Mato Grosso do Sul and Parana.
Following a meeting with the Brazilian president, Justice Minister Marcio Thomaz Bastos is on his way to Sao Paulo to offer the use of both the army and an elite police unit.
Heavily armed gangs held up more than 60 buses during a third night of extreme violence in Sao Paulo, clearing the passengers off and then setting the vehicles alight.
Molotov cocktails were hurled into several bank branches and across Sao Paulo city, police stations again came under attack by gangs wielding machine guns, machetes and home-made bombs.
There were also several fatal shoot-outs.
On Monday morning, bus terminals and underground stations were closed amid fears of further attacks, making it impossible for many people to get to work. Many worried parents kept their children away from school.
The attacks and riots began on Friday after 700 jailed PCC members were transferred to higher-security facilities.
Violence was reported in various parts of Greater Sao Paulo, as well as towns along the coast, including Guaruja, Santos and Cubatao, and towns in the interior of the state.
Despite the violence, the governor of Sao Paulo state, Claudio Lembo, has said local authorities can cope, but Brazilian newspapers report that the federal government is eager to send troops to restore order.
A local public safety official told the Associated Press that authorities had been prepared for a PCC response to the jail transfers but "never imagined it would be so big or ferocious".
According to authorities, 38 gunmen and 39 police officers and prison guards are among the dead.
Those who saw the killing of one police officer said two men wearing masks had approached and shot him in the head as he dined with his wife.
Founded in 1993, the PCC has been involved in drugs and arms trafficking, kidnappings, bank robberies, and prison breaks and rebellions, police say.
The power of the faction has been heightened in recent years by the availability of mobile phones, smuggled through prison security, enabling members to run criminal activities from the safety of their cells.
In November 2003, the gang attacked more than 50 police stations, killing three police officers and wounding 12.
Those attacks were thought to have been orchestrated by PCC leaders in jail.