The last 10 places in the Eurovision final are up for grabs in Thursday's second semi, with Denmark and Australia hotly tipped to make it through once the votes are counted.
Fifteen countries will do battle at the Wiener Stadthalle for the remaining spots in Saturday's showpiece at Austria's biggest indoor arena.
Eurovision is the world's biggest live televised music event, typically reaching more than 150 million viewers, and Vienna 2026 is the 70th edition of the glitzy show where spectacle and drama go hand in hand.
Denmark's Soren Torpegaard Lund, whose background is in musical theatre, is gaining traction with "For Vi Gar Hjem" ("Before We Go Home"), a pop song tinged with electro.
"I'm a big fan of the show and I have been since I was a kid. So, it's crazy to me that I'm here now," he told AFP on Sunday.
Australia has appeared at Eurovision by invitation since 2015, finishing runner-up in 2016.
But the country could go one better this time around thanks to established star Delta Goodrem.
The 41-year-old had a string of international hits in the early 2000s and is singing "Eclipse", evoking a romantic alignment of the planets.
"For those who might have had my music many years ago in their hearts and they've just rediscovered it again, I hope that they would join me in this moment," she told AFP.
"And for those who I've just met, just know that my heart is open to all to be there and to be able to enjoy this timing and music and empower the listener."
Along with Denmark and Australia, Romania and Ukraine are the favourites to progress to the 70th Eurovision Song Contest grand final.
But it could be Goodnight Vienna for Azerbaijan, Luxembourg, Armenia and Switzerland, according to the bookmakers.
Bulgarian pop singer Dara is set to get Thursday's concert under way with "Bangaranga", opening the extravaganza with the lines: "Come alive / Surrender to the blinding lights / No one's gonna sleep tonight / Welcome to the riot."
"Bella" is Malta's first entry to contain the Maltese language since a few lines were used in 2000.
Norway's Jonas Lovv will round out proceedings with "Ya Ya Ya".
The 11,200 tickets for each concert were snapped up by fans from more than 75 countries.
The song contest has a hardcore following and the Eurovision village erected in front of Vienna City Hall has been drawing in fans, with karaoke and photobooths among the attractions.
"I've been a few times and I just love it. We usually go and just make costumes of the people who we like the best," said Croatian fan Sasha.
"Everybody's here for Eurovision and everybody loves it so much. There's no crazy people, there's no idiots who will just like get drunk and make problems. It's always fun, fun, fun," he told AFP.
Austrian fan Markus said part of the joy was "listening to music from countries that we don't usually listen to".
Ten countries made it through from Tuesday's first semi-final.
They included overall favourites Finland, plus Greece, Israel, Sweden and Moldova.
Five countries pulled out of this year's Eurovision over Israel's participation -- the biggest political boycott in the show's history dating back to 1956.
A pro-Palestinian demonstrator who heckled during Israel's performance was thrown out on Tuesday, while three others were also ejected for disruptive behaviour.
Protests are planned in Vienna city during the rest of Eurovision week.
This year, the semi-finals are being decided by public vote and also by professional juries.
Eurovision major financial backers Britain, France, Germany and Italy have guaranteed spots in Saturday's 25-country final, alongside hosts Austria.
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