Brazil received a World Cup boost when Fifa declared that the Curitiba stadium is back on course for completion before the first of its four matches on 16 June.

The announcement lifts one of the biggest concerns facing the tournament organisers, who may have had to reimburse tickets, flights and hotels for teams and fans if the games were moved.

The national sigh of relief was almost palpable after the Fifa assessor Charles Botta judged that sufficient progress has been made in the past month, but football's governing body warned that there was little margin for error and urged the hosts not to slack off.

"Curitiba confirmed as £WorldCup venue, based on the financial guarantees, the commitment by all stakeholders & progress made," Fifa tweeted on its official account. "It's a race against a very tight time line. Collective effort by all stakeholders involved in Curitiba must continue at highest pace."

The Arena da Baixada is still far from complete. Images from the stadium showed scaffolding, cranes, cement mixers and workers wandering through piles of cement and stone.

The owners Atletico Paranaense said it is now 91% finished and work has accelerated sufficiently in the past month to ensure that the ground will be ready for its opening game – Nigeria against Iran.

The "D-Day" announcement – as it has been dubbed – came as the coaches of the 32 World Cup participants met in the southern city of Florianapolis for a technical seminar on logistics and facilities.

A month ago, Fifa's secretary general, Jérome Valcke, warned Curitiba that it has just four weeks to shift construction gears or risk being thrown out of the tournament. "We cannot organise a match without a stadium, this has reached a critical point," he said at the time. "Not only is it very behind in its construction, but it has failed to meet any of the deadlines set by Fifa," he said at the time.

Fifa had reportedly begun looking into substitute venues. According to the Brazilian media, Porto Alegre, which is about 400 miles away, was put on standby.

This is far from the only problem facing the hosts. http://www.theguardian.com/world/2014/feb/16/brazil-world-cup-disaster-delays-protests-deaths facing the organisers as the countdown clock ticks closer to the tournament kick-off on 12 June.

Last week saw the sixth fatality at a stadium construction site. Antonio José Pita Martins, was crushed in Arena da AmazÙnia in Manaus, where three people have now died preparing the stadium where England will play their opening match against Italy. It has also emerged that a fire at the Cuiaba stadium in October had done structural damage despite promises by state officials that the impact was minor. An 18-page report by the Mato Grosso state Public Ministry warned that the blaze caused "structural damage" that "could compromise the overall stability of the construction," according to Reuters. The sports ministry has promised to look into the matter.