As fog billowed, a giant cloaked figure strode onto the Eurovision Song Contest stage, lightly cradling Ukraine's singer, Zlata Ognevich, who looked tiny and doll-like in his arms.

The stunt awed the audience as Ukraine performed its entry during the contest semi-final on Tuesday. The ballad, called "Gravity", is widely tipped to win third place in Saturday's final in Malmo, Sweden.

The mysterious man in the fairy-tale costume is Ukrainian-born Igor Vovkovinskiy, who at 7 foot, 8.33 inches (2 metres 35 centimetres) is now the tallest man in the United States.

Now 30, Vovkovinskiy was born in the Vinnytsia region of central Ukraine but moved to the United States at the age of seven to gain treatment for the hormonal abnormality that caused his growth spurt.

Ukraine's contestant Ognevich has praised Vovkovinskiy as the highlight of her stage show.

"My director looked all around the world for a fairy-tale giant. He chose Igor because he fits the role of a good-natured fairy-tale giant better than anyone else," Ognevich told Komsomolskaya Pravda in Ukraine daily.

Vovkovinskiy is a law student but is also keen to break into acting and has appeared in several commercials as well as a small role in the 2011 comedy film "Hall Pass."

During the latest US presidential campaign won by Barack Obama, he won fame by proclaiming himself the "World's Biggest Obama Supporter".

His popularity in the US -- and now thanks to Eurovision also in Europe -- does not help with everyday problems related to his extraordinary growth, such as needing to buy all his clothes and shoes made-to-order.

In an interview with Russia's LifeNews website, Vovkovinskiy's mother Svetlana said that he underwent surgery in the US and has sought treatment around the world, but no one has been able to name the exact cause of his condition.

"What happens is that once in a millennium a giant is born," she said.

"As the fairy tales say, he grew in leaps and bounds. At first we thought this sort of thing only happened in fairy tales, but when we found ourselves faced with it, we realised that there is a grain of truth in every fairy tale."

Vovkovinskiy describes himself as "a good-tempered giant" on the website of Ukraine's contestant and jokes that the song's title of "Gravity" strikes a chord with him.

"Gravity is particularly evident for such a big man like me but I know how to overcome it," he says.

While Eurovision is nominally about song quality, every country aims to wow a television audience of more than 100 million for the final with visual fireworks.

In other colourful performances this year, Finland's pro-gay marriage entry ends with a lesbian kiss, while Azerbaijan's entry features a dancer trapped in a plastic box.

Ushering in an era of high-scoring Slavic entries, Ukraine won Eurovision in 2004 with a rousing ballad called "Wild Dances" performed by Ruslana.