Russia kicked off their World Cup in style on Thursday, thumping Saudi Arabia 5-0 in front of an ecstatic crowd in Moscow after President Vladimir Putin officially opened the tournament.

Putin told the 80,000-strong crowd at the Luzhniki Stadium before the match kicked off: "I congratulate all of you at the start of the most important championship in the world."

"Love for football unites the entire world in one team, regardless of people's language or ideology," Putin said to thunderous cheers.

Then, to the delight of the home fans, Iury Gazinsky headed Russia in front in the 12th minute after a cross from Aleksandr Golovin. Substitute Denis Cheryshev rifled home a second shortly before half-time.

Another substitute, Artem Dzyuba, made it 3-0 with about 20 minutes remaining, putting the game out of Saudi Arabia's reach.

Cheryshev scored a stunning goal with the outside of his left foot in time added on and Golovin sealed the rout with a goal direct from a free-kick.

Victory for Russia, ranked a lowly 70th in the world -- three places below Saudi Arabia -- was vital for the home nation's hopes of progressing, with tougher games against Egypt and Uruguay to come.

Earlier, British pop star Robbie Williams caused a stir during his performance at the opening ceremony by making an obscene gesture to a camera.

The former Take That star raised his middle finger at the end of his performance at the Luzhniki after appearing to mouth the words "I did this for free".

Russia is spending more than $13 billion (11 billion euros) on hosting football's showpiece, the most important event in the country since the 1980 Moscow Summer Olympics.

The buildup to the tournament has been dogged by controversy and diplomatic scandals and has shone a light on the challenges facing the country.

On the day of the curtainraiser, Russia freed the main opposition figure to Putin, Alexei Navalny, from jail after he served a 30-day sentence for organising an illegal protest.

But British gay rights activist Peter Tatchell was arrested for holding a one-man protest against the country's record on gay rights, hours before kick-off.

The World Cup favourites -- Germany, Spain, France, Brazil -- enter the fray from Friday onwards.

Brazil and their superstar Neymar are seeking a sixth global crown while Germany, who won their fourth World Cup in Brazil four years ago, will be determined to draw level with the Brazilians.

France boast possibly the most talented squad while Lionel Messi is desperate to make amends for Argentina's defeat in the 2014 final.

The preparations of 2010 winners Spain are in tatters after coach Julen Lopetegui was sacked just two days before their opening game on Friday against Portugal. He had angered his federation by taking the job of Real Madrid manager.

Neymar, the world's most expensive player, has recovered from a broken bone in his foot in time.

Egypt's coach said prolific striker Mohamed Salah is "almost 100 percent" to play in their opening match against Uruguay on Friday after he had intensive treatment on the shoulder injury he suffered playing for Liverpool against Real Madrid in the Champions League final.

The money lavished on the tournament will boost Putin's already sky-high prestige at home by giving many of the 11 host cities their first facelifts in generations.

The tournament also offers Putin a chance to project Russia as a global player that is accepted and respected even while being at odds with the United States.

He is attempting to do so despite Russia being hit by international sanctions following its invasion of Ukraine's Crimea in 2014.

Moscow's military backing of the Syrian regime and alleged meddling in the 2016 US election on President Donald Trump's behalf only deepened its worst rift with the West since the Cold War.

Putin hopes the most-watched event on the planet provides Russia with the "soft power" needed to capture a sceptical world's hearts and minds.

- Racism and riots -

Russian authorities have gone to great lengths to ensure nothing soils the country's image.

Neo-Nazi hooligans who organise mass fights in forests and chant racist slurs at players have been a feature of Russian stadiums for years.

The anti-discrimination network Fare said Russia's football federation was making matters worse by punishing those who reacted to racist abuse "while ignoring the perpetrators".

Security services have either locked up or restricted the movements of hundreds to make sure they do nothing to tarnish Russia's image.