Rio's riotous Carnival was in full swing on Monday as top samba schools paraded sumptuous allegorical floats and hundreds of exquisitely costumed performers to a thumping drum beat.

The night parades in Rio's hallowed Sambadrome marked the high point of the pre-Lent bacchanalian Carnival festival, which is bringing this racially diverse country of 191 million people, virtually to a stop.

Making its first appearance in the elite group of samba schools vying for the title of Carnival champion this year, Renascer, from the western district of Jacarepagua, led the way.

It chose as a theme to showcase the life and work of Brazilian artist Romero Britto, a Recife-born painter and sculptor viewed as an icon of world pop culture who combined influences from cubism with pop, to create a vibrant, iconic style.

Renascer illustrated the artist's style with dazzling costumes representing colorful butterflies, flamingoes and giraffes.

Next came Portela, one of the city's oldest schools, which paid tribute to the late Samba singer Clara Nunes and through her to the rich African cultural and religious heritage of the northeastern state of Bahia.

Led by percussionists of the Sons of Gandhi street band and with its trade mark golden eagle as a symbol, the school portrayed in dances and songs what is most important to the people of Bahia: faith, happiness, hope, belief and devotion.

Seven top schools were showing off their best performers in the renovated sambodrome's 720-meter-long (2400-foot) avenue in front a capacity crowd of 72,500 people.

In the crowd was US singer-actress Jennifer Lopez, resplendent in red pants and matching top.

Bahia was also honored by the Imperatriz school, which chose to explore the life and cultural legacy of the great Bahian writer Jorge Amado.

Salvador, the capital of Bahia, is currently celebrating the 100th anniversary of the birth of Amado, whose books have beem translated into 49 languages and popularized in film, notably "Dona Flor and her Two Husbands".

Mocidade, one of Rio's oldest samba schools and well-known for futuristic creations, was to honor the late popular Brazilian painter Candido Portinari.

Porto da Pedra was to follow by presenting an unconventional theme -- a celebration of dairy products as part of a healthy diet.

Beija-Flor, the 2011 winner known for its creative extravagance and powerful colors, planned to tell the story of Sao Luis, the capital of the northeastern state of Maranhao.

And Vila Isabel was to close the night with a another tribute to Brazil's rich African heritage, particularly its strong connection with Angola.

Six other schools are to parade Monday night as part of the hotly contested event to pick the Carnival champion, judged on choreography, music, dancing and creativity.

Preparation for the Sambadrome parades starts months in advance, as each samba school mobilizes thousands of supporters who must create the various parts of the school's display.

Those parades have a special meaning for residents of Rio's impoverished shanty towns, or favelas, for whom samba -- a dance which African slaves brought to this country -- stirs passions as strong as soccer.

Favela residents are often members of a local samba school and are deeply involved with the performance and preparation of costumes.

It turns the spotlight on the artistic talent, creative genius and zest for life found in those predominantly black shantytowns which often lack running water, electricity and sewage systems.

Sambadrome seats cost between $50 and several thousand dollars, depending on whether one sits on packed benches in the open or in air-conditioned VIP boxes stocked with champagne.

The Rio Carnival, billed as 'the greatest show on Earth', generates 250,000 jobs and revenues of $640 million for hotels, bars and restaurants, according to state estimates.

The cream of Brazil's society and its most famous stars are keen to be seen at the Sambadrome parades. Big-name companies invite luminaries, including foreign celebrities, to their Sambadrome skyboxes overlooking the processions to promote their brands.

Carnival is celebrated with equal gusto in other cities and towns, including Sao Paulo, Brazil's economic capital and Latin America's most populous city, and Salvador, the heart of the rich Afro-Brazilian culture.