MEXICO CITY : The World Cup kicks off on Thursday with FIFA betting that the enduring appeal of the greatest footballing show on earth can rise above mounting anger at ticket prices and a US immigration crackdown that has seen fans, a top referee and team officials barred from the tournament.

A record 48 teams and millions of fans are set to descend on the United States, Canada and Mexico for the first World Cup co-hosted by three nations, the largest and most logistically complex edition of the tournament ever staged.

The action gets under way at Mexico City's iconic Estadio Azteca on Thursday, with co-hosts Mexico taking on South Africa at 1:00 pm local time (1900 GMT), launching a sprawling, nearly six-week-long spectacle that will culminate in the final at New Jersey's 82,500-seat MetLife Stadium on July 19.

Can Lionel Messi, at the age of 38, settle any lingering debate about his status as the greatest player of all time by leading Argentina to a second consecutive World Cup title?

Or can Messi's great rival, the 41-year-old Cristiano Ronaldo, defy father time by inspiring a talented Portugal team to its maiden World Cup win?

Those questions and more will be answered over the course of a tournament that Gianni Infantino, the president of world football's governing FIFA, has bullishly hyped as "the greatest show that the planet has ever seen."

- Ticket fury -

Yet Infantino's breezy assurances have run into hurricane-force headwinds of scepticism during a build-up dogged by concerns over affordability, politics and conflict in the Middle East.

The skyrocketing cost of tickets has triggered a global backlash which has left FIFA and Infantino struggling to mount a convincing public relations defense.

The most expensive ticket for the 2022 World Cup final in Doha cost around $1,600 at face value; in 2026 the most expensive face value final ticket being sold by FIFA is an eye-watering $32,970.

That kind of stratospheric inflation has been prevalent across the tournament's 104 matches, where seats for many games remain available on secondary re-sale markets despite huge demand.

Even Infantino's staunch ally, Donald Trump, has balked at the cost, reacting with surprise when told of the $1,000 price tag for tickets to the USA's opening game with Paraguay in Los Angeles on Friday -- the first game on US soil.

"I wouldn't pay it either, to be honest with you," the US president told the New York Post last month.

Mexico's President, Claudia Sheinbaum, who is grappling with teacher protests in Mexico City that threaten to disrupt Thursday's opener, has meanwhile said she will not attend any games in Mexico.

- 'Exclusion and fear' -

Other critics have questioned whether the World Cup party will be soured by the tense political climate in the United States.

Human Rights Watch says the Trump administration's immigration, demonstrations and press freedom could lead to a World Cup defined by "exclusion and fear."

Those concerns were given a fresh jolt of momentum on Monday when FIFA confirmed that Somali referee Omar Artan would play no part in the tournament after being denied entry to the United States.

Artan was turned back when he arrived at Miami International Airport on Saturday over what US authorities said were "vetting concerns."

The Somali official was just the latest in a growing list of people who have been barred from entering the United States for what Infantino has billed as the "most inclusive" World Cup in history.

The US-Israel military strikes launched against Iran in February have also loomed large over the tournament, where Iran are due to play three group games in the United States, starting with their opener against New Zealand on Monday.

Iran have switched their base camp from Tucson, Arizona to the Mexican city of Tijuana.

While Iran's players are free to travel in and out of the United States, some 15 administrative and management staff have been denied visas by US authorities in a move Iranian authorities have condemned as "deliberate and discriminatory treatment."

Fans have also fallen foul of US immigration policies, with a group of Scotland supporters having their entry permits revoked at the last minute.

- Expanded field -

On the field, the decision to expand the tournament to 48 teams -- up from 32 in 2022 -- is likely to strip the group stage of any sense of jeopardy.

The tournament will see a range of other innovations.

For the first time in World Cup history, every game will feature cooling breaks in the middle of each half, a measure designed to mitigate the effects of searing heat and humidity expected at many of the tournament's 16 venues.

Players and referees will need to adjust to several new rules being rolled out at the World Cup, including teams being required to make substitutions inside 10 seconds to prevent time-wasting.

A crackdown on racist abuse will see players risk a red card for covering their mouth with a hand, arm or shirt during a confrontation with an opponent.