However, Muto told a press conference that cancelling the Games this summer had not entered his thoughts. “I want to again state clearly that cancellation or postponement of the Tokyo Games has not been considered,” he said.

Japan, which announced its first death from the outbreak on Thursday, has one of the fastest rates of infection outside China, where 60,000 have fallen ill.

Ashton believes the Games can still take place, but said ruling out postponement was dangerous. “You’ve got to think the unthinkable,” he said. Playing down the risk unnecessarily, he added, was “counterproductive and you end up with exactly what you tried to avoid. You end up with panic because people worry about what they are not being told and what is being held back”.

It is less than five months before Team GB’s athletes travel to set up camp ahead of the Games, which begin on July 24.

The statement from Muto appeared to contradict his comments last week in which he stated he was “extremely worried in the sense that the spread of the infectious virus could pour cold water on momentum for the Games”.

The World Health Organisation refused to be drawn on Muto’s latest comments, but Michael Ryan, executive director of the health emergencies programme, said in a statement that “there’s no zero risk with any mass gathering”.

He added that the WHO “cannot become the arbiter of that process” but “all meeting organisers have to put in place a risk-management strategy in the context of there never being a zero risk”.

Ashton, meanwhile, who directed the response to the Legionnaires outbreak in Barrow-in-Furness in 2002, said “contingency plans” were critical. “I’m not saying this postponement is going to happen at all, but it’s about steering a path between alerting people so that we can be prepared and forearmed, but also avoiding panicking people,” he said. “I think there’s no way they would stop it right now, but they need to have a plan of what they would do if it does build up momentum over the next five months. They might have to have events without audiences. Who knows?”

Failing to plan for the Games being cancelled was “childlike”, he added, as other epidemics had lasted a year or more. “The sporting organisations must be thinking the unthinkable, that’s my advice.”

Athletics have already taken a major hit from the virus, with next month’s World Indoor Championships in Nanjing cancelled. The second and third Diamond League meetings of the season in May are also due to be in China, and are understood to be under review.

Golf’s China Open, meanwhile, is expected to be cancelled within days, after players and caddies were advised to delay booking flights.

“We are monitoring the situation in China closely and are in consultation with all stakeholders of the Volvo China Open,” a Tour spokesman said. “As with all our tournaments, the well-being of players, spectators and staff remains our absolute priority. We expect to make an announcement shortly.”

Outside China, there have been 447 cases in 24 countries. At least nine have fallen ill in the UK and Ashton said domestic sporting bodies must now play their part in helping contain the spread.

He said the Premier League, English Football League and other major domestic sporting events should focus particular efforts on improving hygiene around lavatories, suggesting immediate moves to install more antibacterial gel machines at grounds.

“They really need to review their hygiene and sanitary arrangements because quite often the lavatories are awful at grounds, the arrangements for soap and water, too,” Ashton said. “One of the real issues we have is poor hygiene in grounds and I think clubs should dedicate a page in their programmes as reminders on the importance of washing hands, things like that.”

Ashton, former Regional Director of Public Health in the North West of England and co-founder of the WHO Healthy Cities Project, gives his account of public health in the UK and beyond in, Practising Public Health, published by Oxford University Press. Paperback £29.99 on Amazon.