Teams of men pushed Carnival floats the size of buses up Presidente Vargas Avenue toward the Sambadrome, an open-ended stadium that hosts the spectacular parades by Rio's top samba groups on Sunday night.
Although the street parties where revelers drink and dance day and night are the heart of Rio's Carnival, the extravaganza in the Sambadrome on Sunday and Monday nights is the highlight of the celebrations.
Each of the 12 samba groups, known as schools, features an army of as many as 6,000 dancers in richly decorated costumes as well as eight floats, some as high as a three-story building.
Near the Sambadrome, half a dozen industrial cranes stood ready to lift half-naked beauty queens in plumed headdresses atop the floats.
Each school will march for about 75 minutes, marked by judges for their performance in a competition for the champions' crown. Themes this year include the 200th anniversary of the arrival of the Portuguese Royal Family in Brazil and the 100th anniversary of Japanese immigration.
City authorities expect more than 700,000 tourists in Rio for the five days of Carnival, which ends on Ash Wednesday.
A few blocks from the Sambadrome, a few hundred die-hard revelers danced and sang tirelessly on Sunday morning despite lashing rain. Dressed as devils, brides, magicians or simply wearing silly hats, they drank beer and sang traditional Carnival tunes.
"This rain is nothing. Yesterday we were in a street party where they were spraying people from a water hose truck. Now< that was fun!" said Claudia Nogueira, 25 and dressed as a nurse with white lingerie showing from her robe.
Police presence was heavy in the city center, allaying
concerns about a police strike after senior commanders had
offered to quit or were sacked over demands for higher pay and
better working conditions.
Rio is one of Latin America's most violent cities. But Carnival -- a big source of tourism revenue for the city -- is always safeguarded by thousands of police and outbreaks of violent crime are rare during the festivities.
Much of the violence is related to drug trafficking in the slums, or favelas. Weeks before Carnival, police investigated one of the most popular samba schools, Mangueira, over allegations it was sponsored by a drug kingpin.
The Carnival parade also became a source of controversy as one samba group, Viradouro, was banned from presenting a Holocaust-themed tableau in its parade.
The school has promised a surprise change in its display to protest against what it called artistic censorship. All its floats lined up on the avenue ready for Sunday's parade were covered in black plastic sheeting.
Viradouro had planned to feature a pile of model dead bodies on a float with an Adolf Hitler figure standing over them. A judge barred the display on Thursday after Jewish groups filed a petition saying it was inappropriate to commemorate the genocide of the Jews by Nazi Germany in a parade with semi-naked dancers.