The fight against racism in Brazil was the theme of samba group presentations and street parties as the Rio de Janeiro Carnival entered its second night of over-the-top festivities.

Some samba groups put together dance numbers to honour Afro-Brazilian heritage and one built a giant Nelson Mandela float to remind people of his fight for equality, while calling for more racial integration in the South American country.

To start the second day of the Carnival shows, thousands of performers carpeted the entire half-mile street with fluorescent orange-and-yellow costumes and Halloween-like floats of tarantulas and Jack the Ripper.

Tens of thousands of people gathered on both sides of the imposing sambadrome to watch and sing along to the blasting music.

Top-tier samba group Imperatriz Leopoldinense said it was inspired by an incident of racism in football, when a banana was thrown at Barcelona star Dani Alves during a match last year against Villarreal in Spain.

The Brazilian Alves ignited a movement against racism in soccer after he was seen coolly picking up the banana and eating it before taking a corner kick.

Imperatiz, in its samba parade, alludes to that incident with a performer playing a black-and-white harlequin inside a peeled banana.

"People think that discrimination in Brazil is a thing of the past," said Andre Bonatte, who helps co-ordinate cultural affairs for Imperatriz.

"But we are here to say it is not like that. There are still many racist displays in our society."

Critics say black face make-up during Carnival is one such display. Some people have complained this year of Carnival street parties where people black up, including one called Luxury Maids in which white men wear black make-up, Afro wigs and dress as servants.

"It is shocking that something so explicitly and ridiculously racist is being treated as a funny tradition worth preserving," wrote columnist Jarid Arraes.

Felipe Ferreira, a professor who heads the Carnival Reference Centre at the Rio de Janeiro State University, says the origins of the samba groups stem from people brought as slaves from Africa who thought of mixing their customs of playing drums and tambourines in the streets with the more extravagant European parties.

"The aspect of racial integration and the meeting of different cultures was something that samba schools initially promoted," said Mr Ferreira. "This seems to be a return to the ideal."