The samba-dancing crowd filled the streets of Rio's business district and some passed out under the summer heat...
The samba-dancing crowd filled the streets of Rio's business district and some passed out under the summer heat.
Police arrested more than 100 partygoers for minor crimes, but the majority of celebrations were peaceful, officials say.
About 700 other street parties and the world-renowned samba schools' parade will take place in Rio until Tuesday.
The Cordao do Bola Preta 95th annual street parade kicked off at 1000 (1400 GMT) on Saturday.
Thousands, many wearing costumes, danced as live bands on lorries played tunes of traditional carnival songs and samba school themes.
The crowds converged in the early afternoon, and many revellers climbed onto parked police cars, as the massive street party drew to a close.
One of the cars had its windscreen smashed in and more than 100 were detained by the police, mostly for urinating on the streets, the authorities said.
Hundreds of other street parties are happening in Rio, many simultaneously in different parts of the city.
The samba schools competition , with its sophisticated floats and costumes, is set to happen in Rio's Sambadrome between Sunday and Monday.
The carnival is set to draw 1.1m tourists to Rio, generating some $650m (__410m) for the local economy. Hotels and restaurants are booked almost to capacity.
International stars such as US actor Will Smith, rapper Kanye West and actress Megan Fox are already in the city for the celebrations.
Brazil's annual carnival kicked off on Friday, but the parades and street parties had a sombre tinge, coming after a nightclub fire that killed 238 people.
Mourning rituals continued as the mayor of Rio de Janeiro handed over the keys of the city to carnival ceremonial figurehead King Momo.
President Dilma Rousseff attended a memorial Mass for the fire victims at Brasilia's cathedral on Thursday night.
She is not taking part in the five-day party, spending it in Bahia state.
More than 60 casualties of the inferno remain in hospital, and many cities - particularly near the southern city of Santa Maria where the fire happened - have scaled down their festivities as a result.
For Brazil, Carnival 2013 is an important test of the city's infrastructure ahead of the big sporting events lined up for the future, including the World Cup in 2014 and the Olympics in 2016, says the BBC's Julia Carneiro in Rio.
BY BBC News