RIO DE JANEIRO - A huge float carried by an out-of-control truck at the Rio de Janeiro samba parade struck at least 12 people, seriously injuring two.

The accident on Sunday, which coincided with heavy drizzle, marred the start of the all-night samba dance-off at the Sambadrome stadium.

The truck, topped with one of the extravagant floats that symbolize the world's most famous carnival, was at the tail end of the Paraiso do Tuiuti samba school parade - the first of six schools competing overnight.

It drove too close to a fence at the entrance to the competition piste, leaving several people unable to escape. One woman, a news photographer, had a leg badly crushed.

Despite the incident, the party soon got back in swing.

Brazilians living through two years of steep recession and nearly 13 percent unemployment have grasped this year's carnival as a chance to let off steam. In Rio especially, the thrill of hosting the Olympics six months ago has given way to the grim reality of rising crime and near bankruptcy of the state government.

So there were intense cheers around the packed stadium of 70,000 people the moment that drumming began to thunder up from the piste.

Samba queens dressed in sequined micro-costumes and vast feathered headdresses danced at dizzying speed. Behind them came armies of drummers and costumed dancers, interspersed by the floats.

Each school picks a theme for its parade and is judged according to strict criteria. Another six schools were scheduled to parade on Monday night, with the champion being announced on Wednesday.

The most daring parade was from the samba school known as Imperatriz Leopoldinense, which chose the destruction of Brazil's majestic Amazon rain forest as its theme.

Schools typically pick politically safe themes, often paying homage to Brazilian musicians. Paraiso do Tuiuti, for example, honored the 50th anniversary of the "Tropicalia" musical movement.

But Imperatriz Leopoldinense waded into the debate over indigenous rights and the future of the ever more under pressure Amazon.

The parade has infuriated members of the powerful agribusiness sector. The Brazilian Association of Cattle Breeders called the parade "unacceptable".

Rio is Brazil's carnival capital. Tourism officials told Globo newspaper on Sunday that as many as 1.5 million tourists have descended on the city, the best result in eight years, injecting some $960 million into the local economy.