Switzerland's Nemo won the Eurovision Song Contest on Saturday, becoming the first artist identifying as non-binary to claim victory, in a competition marked by controversy over Israel's participation during the war in Gaza.

Twenty-four-year-old Nemo's "The Code" won the highest score from nations' juries, and enough of the popular votes to get 591 points, edging out Croatia in the final, held in Sweden's Malmo.

"I hope this contest can live up to its promise and continue to stand for peace and dignity for every person in this world," a teary-eyed Nemo said while receiving the trophy.

Nemo's journey towards realising their non-binary gender identity served as inspiration for the highly personal winning entry.

"'The Code' is about the journey I started with the realisation that I am neither a man nor a woman," Nemo said.

In Zagreb, a crowd gathered at a square to follow Croatia's Baby Lasagna, who finished second with 547 points.

Twenty-five nations competed Saturday but much of the focus has centred on the controversy of Israel being able to take part.

When Golan went on stage to perform her "Hurricane", both cheers and boos could be heard from the audience in the Malmo Arena.

Outside the arena, police pushed back protesters where more than a hundred demonstrators waved flags and chanted "Free Palestine".

Diverse Malmo is home to the country's largest community of Palestinian origin and according to police at least 5,000 people gathered to protest in the city in the afternoon.

The European Broadcasting Union, which oversees the event, confirmed in March that Golan would take part, despite calls for her exclusion from thousands of musicians around the world.

The same month, contestants from nine countries, including Nemo, called for a lasting ceasefire. (AFP)