Botswanan runner Isaac Makwala was barred from entering the London Stadium after he and a number of other World Championships athletes were struck down with food poisoning.
ITV News accompanied Makwala, a gold medal hopeful, as he was stopped by security hours ahead of his 400m World Championships final.
The Botswanan competitor was forced to withdraw from the 200m heats on Monday night after suffering from gastroenteritis.
He was one of a number of athletes forced to pull out following the outbreak of illness.
His chances of competing in Tuesday's 400m final looked increasingly slim as Makwala was barred from entering the stadium and instead directed to the offices of the IAAF, as ITV News witnessed.
Irish hurdler Thomas Barr was also forced to pull out of his semi-finals after being struck down with the vomiting bug.
"I'm gutted...my whole year has been focused on the World Championships," he said.
"Not being able to go out and compete...is beyond disappointing."
Public Health England confirmed around 30 people staying in official hotels had reported illness.
Of these two were confirmed as norovirus.
No British athletes have been affected.
ITV News Sports Editor Steve Scott said the illness outbreak was a "blow" for the athletes affected and could also become "very serious" for the games.
Scott warned that the outbreak could have an affect on the championship's reputation if the crisis escalated and "defined the games in the long term".
A statement from London 2017 read: "There have been a number of cases of gastroenteritis reported by team members residing within one of the official team hotels for the World Championships.
"Those affected have been supported by both team and LOC (local organising committee) medical staff, in addition we have been working with Public Health England to ensure the situation is managed and contained.
"As a result, further advice and guidelines have been issued to team doctors and support staff - standard procedure for such an occurrence where a number of teams are occupying championship accommodation."