Over the next days this racially diverse country of 191 million people will come to a standstill for the pre-Lent bacchanalian festival that is its most popular holiday.
As in previous years, Salvador de Bahia, Brazil's third largest city and the heart of the rich Afro-Brazilian culture, led the way, with hundreds of thousands of revelers people pouring into the streets late Thursday to dance and party.
The theme for this year's Carnival in Salvador is "The Carnival Country," the title of a 1931 novel by Jorge Amado, in homage to the late Bahian author as the city marks the 100th anniversary of his birth.
But the global spotlight will be on Rio Friday when the "Marvelous City" kicks off its Carnival extravaganza, world-famous for its sumptuous parades of elaborately decorated fantasy floats and scantily-dressed women.
The five-day mega-event will be broadcast live around the world.
Carnival in Rio generates 250,000 jobs and revenues of some $640 million for hotels, bars and restaurants, according to state officials.
City officials expect more than than five million people, including 850,000 tourists, to attend.
There had been fears that unrest in Brazil's state police force might disrupt the Carnival festivities in Salvador and Rio, but police strikes in those cities were settled just in time.
Milton Junior -- better known as King Momo, the Rio Carnival's chubby symbol of excess -- will be crowned Friday and will receive a giant key to the city, symbolically launching "greatest show on earth."
Joyous street parties with soaring beer consumption will follow and will climax with the eagerly-waited parades in the "Temple of Samba" as the renovated Sambadrome is known.
Thirteen competing samba schools will march hundreds of lavishly costumed singers, dancers and musicians down a specially designed parade route leading to the Sambadrome.
Originally designed 30 years ago by famed Brazilian architect Oscar Niemeyer, the facility reopened last Sunday after a nine-month makeover.
It now boasts an expanded 72,500-seat capacity, with access ramps for the handicapped and elevators.
Rio's top samba schools will vie for the title of carnival champion, a dazzling contest watched with the same fervor as football games in this soccer-mad nation.
Each school spends between two and five million dollars to organize its parade. Some are believed to be funded by gambling syndicates.
Among foreign guests will be US celebrities Jennifer Lopez, singer Fergie and Playboy founder Hugh Hefner.
Security-conscious authorities are deploying 50,000 police officers to patrol the streets along with a small, remote-controlled blimp fitted with a camera to keep watch over street parties.
Rio state officials are also distributing more than three million free condoms to the revelers, along with 55,000 condom cases and 160,000 leaflets with information on how to prevent sexually transmitted diseases.
With millions of revelers set to hit the streets of Rio, Brazilian Health Minister Alexandre Padilla on Thursday warned that the city faced a major dengue epidemic.
"I believe that Rio could this year face one of the worst dengue epidemics in its history, in terms of number of cases," Padilla said in a television interview.
While the mosquito-transmitted dengue virus strain prevalent in Rio was neither the most serious nor fatal, it was the least common in Brazil, so "a larger number of people are more vulnerable" to infection, Padilla said.
The official Agencia Brasil said since the start of the year, 3,499 dengue cases have been recorded in Rio, compared with 2,322 last year, but none were fatal.