PHOTOS: 100-day Brazil World Cup countdown begins!

With 100 days to go before the World Cup starts, Brazil is in the home straight of the countdown and huffing and puffing to complete stadiums, airports, IT networks and public transportation systems.

Four of the 12 venues are still not ready and at least two will not be completed until at least April, two months before Brazil meet Croatia in the opening match on June 12.

Authorities are also racing against the clock to finish airport terminals and transport systems and to clean up areas around the grounds.

Officials at soccer's ruling body FIFA have expressed concern but can do little more than cross their fingers and hope everything is alright on the night.

"I am not a World Cup specialist but I will say this has not been easy for sure," FIFA secretary general Jerome Valcke told reporters in Zurich at the weekend.

"I think things will work well but it is also true that whenever you receive something late it becomes a challenge to make it ready in time."

Valcke, the man charged with organising the tournament, prompted a diplomatic uproar in 2012 when he said Brazil needed "a kick up the backside".

President Dilma Rousseff replied by vowing this would be "the World Cup to end all World Cups", a slogan repeated by FIFA boss Sepp Blatter, but others say there are reasons for scepticism.

Two of the completed arenas have already shown signs of wear and tear, with part of the roof at the Mineirao stadium in Belo Horizonte falling off at the weekend. No one was hurt in the incident.

"Only when stadiums are completely ready can you train people to work inside them," said Jose Roberto Bernasconi, president of the National Association of Architectural and Consulting Engineering Companies.

"There are stewards, security, plumbers, fire safety officers. When you have 65,000 people inside the ground including kings, presidents, prime ministers, everything has to work.

"Remember when Heathrow opened Terminal Five a while back?", asked Bernasconi of the London airport. "They lost hundreds of bags.

"That's not unusual at the start. These things need to be tested."

One of the reasons for the late rush is Brazil's delay in making key decisions.

The only country to lift the World Cup five times, Brazil won the right to host the competition in 2007 but took almost two years before deciding the host cities.

It also delayed the building of the infrastructure that is vital not just for the World Cup but also necessary if the South American nation is to keep growing.

Brazil has grown hugely over the last decade and more than 30 million people have emerged from poverty to move into the consuming classes.

However, experts say not enough money has been invested in the infrastructure needed to keep up with that expansion.

At least one airport will welcome passengers in canvas tents because new terminals are not ready.

Some host cities will declare public holidays on matchdays in a bid to cut down traffic on already congested streets.

Five cities abandoned plans to add bus lanes, underground lines or trams and several scaled back their promised investment while telecommunications networks and media centres can only be added once the stadiums are complete.

"We still have to instal all the IT solutions for the media," said Valcke. "Without IT and without the telecommunications in place in the stadium you will say we are the worst organisers and it was the worst event.

"To instal the IT in a stadium it needs at least 90 days and we have to work for all the people who have an interest."

There is certainly interest from fans. So far 1.5 million tickets have been sold, more than half of them to Brazilians, a record at this stage.

Authorities expect three million Brazilians to travel to see games and another 600,000 foreigners to visit during the month-long jamboree.

The hosts have exasperated FIFA, with Blatter recently praying to "God, Allah, whoever" to ensure everything is ready in time, and Valcke once again had to put on a brave face this weekend.

"It is very last-minute work but it will work in the end," Valcke said. "You will have what you expect and the teams will have the best."