RIO DE JANEIRO • Rio's Carnival - a five-day festival of dancing, bared flesh and wild costumes - is under way, in the face of warnings that the Zika virus might make even kissing dangerous.

Rio's mayor, Mr Eduardo Paes, handed a big golden key to the city to the carnival's ceremonial ruler, King Momo, who promised a spectacular show.

"With great happiness, brotherly love and peace, I declare the best carnival on earth open - our Carnival in the Marvellous City," the dancing king, who is elected ahead of the festivities, said on Friday.

The annual mega bash, famed for lavish - and skimpily dressed - samba parades and all-night street dancing, is expected to attract as many as five million people.

In Sao Paulo, Brazil's most populous city and its economic capital, carnival celebrations were kicked off under intermittent summer rain.

This year's carnival across Brazil starts under the cloud of the mosquito-transmitted Zika virus, which normally results in few ill effects, but is blamed for an outbreak of serious birth defects in babies born to mothers infected while pregnant. The growing alarm over Zika - and uncertainty over how the virus can be transmitted - comes at the worst time for Rio, where about one million tourists are expected to join millions of locals at parties and parades.

In August, Rio will become South America's first city to host the Summer Olympics, and there are mounting fears that the mega event will be disrupted.

Foreign governments are lining up to urge tourists to avoid countries having the Zika-carrying mosquitoes, and Brazil itself has specifically advised pregnant women not to come to the Olympics.

The carnival peaks today and tomorrow night with the competing samba parades at the Sambadrome, famous for their choreography and extraordinary costumes.

AGENCE FRANCE-PRESSE