17:20 03 February 2016
Experts are worried that Zika virus, which has been linked to cases of babies born with underdeveloped brains, is spreading far and fast.
The World Health Organisation (WHO), which said that it poses a global public health emergency, puts Zika in the same category of concern as Ebola. Research and aid will be fast-tracked to tackle the infection.
In Brazil, there have been 4,000 reported cases since October.
WHO director general, Margaret Chan, said: "I am now declaring that the recent cluster of microcephaly and other neurological abnormalities reported in Latin America following a similar cluster in French Polynesia in 2014 constitutes a public health emergency of international concern."
She added that the main priorities are to protect pregnant women and their babies from harm and to control the mosquitoes that are spreading the virus.
Dr Jeremy Farrar, Director of the Wellcome Trust, said: "There is a long road ahead. As with Ebola, Zika has once again exposed the world's vulnerability to emerging infectious diseases and the devastation they can unleash. Alongside the emergency response that Zika necessitates, we must put in place the permanent reforms, health systems strengthening and proactive research agenda that are needed to make the global health system more resilient to the threat of future pandemics."