A disease linked to the Zika virus in Latin America poses a global public health emergency requiring a united response, says the World Health Organization.
Experts are worried that the virus is spreading far and fast, with devastating consequences.
The infection has been linked to thousands of babies being born with underdeveloped brains.
The WHO alert puts Zika in the same category of concern as Ebola.
It means research and aid will be fast-tracked to tackle the infection.