An in-form Italy face Turkey in Rome on Friday as Euro 2020 finally gets underway a year behind schedule and with the coronavirus pandemic casting a shadow over the tournament.

Postponed 12 months ago because of the spread of Covid-19, the European Championship -- with the Portugal of a veteran Cristiano Ronaldo defending the trophy -- is being played for the first time all across the continent, with 11 cities from as far apart as Seville to Baku hosting matches.

Games are being played in front of limited crowds and with stringent health restrictions in place.

In Rome, the Stadio Olimpico will be filled to about 25 percent of capacity, meaning around 16,000 supporters will be present to watch Andrea Bocelli sing "Nessun Dorma" before Roberto Mancini's Italy face Turkey in the first game in Group A.

"Last year we would have had a Euro without fans and now at least we have a number of fans, a percentage of fans which is very important for the Euro because it's a festival of football," UEFA president Aleksander Ceferin told AFP.

Ceferin has previously said holding the tournament was a way of showing the world that "Europe is back". Italy are back too, rebuilt under Mancini after their ignominious failure to reach the 2018 World Cup.

European champions in 1968, Italy are currently on a 27-match unbeaten run.

"We have created a great squad. We want to continue to have fun together and we will try to make it to London. I'm very positive," Mancini said on the eve of the game.

Wembley Stadium in London will host the semi-finals of the 24-team tournament as well as the final on July 11.

As anticipation grows, the build-up has been overshadowed by several positive Covid-19 cases.

Hours before the competition kicked off, Russia announced winger Andrei Mostovoy had contracted the virus and was ruled out of the tournament even before the Russians open against Belgium on Saturday.

Spain's squad were vaccinated on Friday morning by the army at their Las Rozas training headquarters near Madrid following positive tests to two of their players -- Sergio Busquets and Diego Llorente.

Busquets will miss Monday's match against Sweden in Seville but Llorente has subsequently tested negative and can resume training.

Spain even had to name a "parallel" squad of 17 reserve players, fearing a possible wider outbreak in the official 26-man squad.

Sweden forward Dejan Kulusevski of Juventus and midfielder Mattias Svanberg also tested positive, with six reserve players called up on stand-by.

But despite the ongoing threat, the show goes on.

"We all have to adapt to a special situation," Ceferin told AFP in an interview in Rome.

"It's not the usual Euro anyway because it's in 11 countries and on top of it there's a pandemic which makes travelling even more difficult."

The majority of the 11 venues, all in different countries, will only be partially-filled for matches, but Budapest is planning to fill its Puskas Arena to 100 percent of capacity.

Denmark announced it would lift mask rules and allow 25,000 fans, instead of 16,000, to attend games in Copenhagen.

Munich will host just 14,000 fans -- around 22 percent of the Allianz Arena's capacity, the lowest of the stadiums being used.

Dublin and Bilbao were dropped from the list of hosts after being unable to give guarantees they could meet UEFA's requirement of accommodating limited numbers of spectators, but Seville stepped in for Bilbao while Dublin's games went to London and Saint-Petersburg.

On the pitch, World Cup holders France -- with Karim Benzema recalled from a five-and-a-half-year international exile -- are firm favourites to add the continental crown.

They have won it twice before, in 1984 and again in 2000, when they were also World Cup holders.

Their first match is in Munich against Germany on Tuesday.

Holders Portugal, with Ronaldo backed up by a star-studded squad, and Hungary complete a tough-looking Group F.

The other likely contenders include Belgium, who will be without Kevin De Bruyne for their first game against Russia on Saturday after he suffered facial injuries in the Champions League final on May 29.

Earlier on Saturday, Wales take on Switzerland in Baku and Denmark play Finland in Copenhagen.

In England, there are hopes Gareth Southgate's young side could take advantage of playing most of their games at Wembley.

England, who have never before reached a European Championship final, begin their bid against Croatia on Sunday.