The Rio Olympics should be moved or postponed over the Zika crisis, 150 scientists have said.
Just 10 weeks before the Games begin, the group has written an open letter to the World Health Organisation (WHO) saying new findings about the virus make staging the Olympics in Rio "unethical".
One of the signatories, Professor Arthur Caplan, said a postponement of three to six months would allow time for a vaccine to be created.
He added: "What we are learning about Zika is that the strain not only causes birth effects but also has this neurological explosion impact on children. It's more serious than we thought"
"We are also starting to understand that it can cause paralysis, rarely but it can do it, in adults, and we don't yet know how long it lingers in a person".
"To top it all off Brazil has been undergoing economic and political troubles and it's not clear that they're going to be able to do what's necessary to protect both athletes and visitors".
The letter says the Games should be moved or delayed "in the name of public health" after infections in Rio rose despite increased efforts to wipe out the mosquitoes that spread Zika.
The signatories are from more than two dozen countries and include former White House science adviser Dr Philip Rubin.
The letter says: "An unnecessary risk is posed when 500,000 foreign tourists from all countries attend the Games, potentially acquire that strain, and return home to places where it can become endemic".
'Zika risk will drop in August'
WHO has already advised pregnant women not to go to Rio and says travellers should avoid poor and overcrowded parts of the city.
The United Nations agency also predicts the Zika risk will drop in August, with the South American winter resulting in fewer mosquitoes.
But the letter highlights a potential conflict of interest, citing the long-established collaboration between WHO and the International Olympic Committee (IOC).
WHO has yet to comment, while the IOC said it would "always consult the WHO for guidance and advice on health matters".
No Olympic Games have ever been moved from their host city due to medical concerns.
One dissenting voice in the scientific community is Dr Tom Frieden, director of the US Centers for Disease Control and Prevention.
He said: "There is no public health reason to cancel or delay the Olympics".
"The risk to delegations going and athletes is not zero, but the risk of any travel isn't zero. The risk is not particularly high other than for pregnant women".