Rio's famous carnival celebrations have officially kicked off, after Friday morning was marred by more street violence between security forces and drug gangs.
One armed gang of about 30 men initiated a three-hour shoot-out with police on one of Rio's biggest thoroughfares, Brazilian media reported.
A motorist died after being shot at point-blank range by one of the group when he refused to give up his car.
Tens of thousands of armed police - and, for the first time, troops - have been sent onto the streets to help guard Rio de Janeiro's carnival following the wave of violence.
In another incident, 28 terrified passengers on a bus bound for Sao Paulo threw themselves to the floor when their bus was hit by a hail of bullets and a Molotov cocktail.
The Brazilian newspaper O Dia said the Avenida Brasil, a dual carriageway, was "transformed into an inferno: cars screaming off in the wrong direction, a bus on fire and many bullets".
In addition to the man who died, other motorists were attacked and ordered to abandon their vehicles in the incident, which occurred during the early hours of Friday morning local time.
It was the latest in a string of attacks in which over 50 buses have been torched.
On Monday shopkeepers were forced to close their businesses after receiving threats.
The violence prompted the Brazilian Government - headed by Workers' Party President Luiz Inacio Lula da Silva - to deploy military police.
More than 50 buses have been torched
He said the population was threatened by "insecurity, unrest and fear".
Revellers vowed not to let the violence spoil the four days of carnival, a pre-Lent festival of drinking and dancing.
Alex de Oliveira, who - at 135 kilograms (300 pounds) - was elected carnival's Rei Momo (Fat King), received the symbolic key to the city and festivities began.
No soldiers could reportedly be seen as evening approached.
The authorities are blaming the violence on a drugs cartel, the Red Command, which has thousands of heavily armed followers and controls many of Rio's shanty towns.
They say they intercepted the gang's leader giving orders on a mobile phone from inside the maximum-security jail where he is a prisoner.
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Fernandinho Beira Mar, or Seaside Freddy, as the gang leader is known, has now been transferred to another prison in the neighbouring state of Sao Paulo.
With 400,000 visitors expected for the celebrations over the coming days, the city authorities say they are worried the violence could affect Rio's tourist industry.
Rio state governor Rosinha Matheus said 36,000 police officers and 3,000 soldiers would keep the peace under an operation dubbed "Safe Rio".
But our correspondent in Rio, Tom Gibb, says most visitors seem to have taken little heed of the stories of violence.
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Major Gilberto Tenreiro of Rio's tourist police said he thought the worst was over.
"The violence was a phase that has already passed," he told news agency Associated Press.
"We are doing everything to make sure tourists can enjoy carnival without any worries."