The World Health Organization has issued a warning that the Zika virus linked to a microcephaly outbreak in Latin America could soon spread to Africa and Asia, Reuters reports.

The WHO has launched a global response unit against the new emergency.

"We've now set up a global response unit which brings together all people across WHO, in headquarters, in the regions, to deal with a formal response using all the lessons we've learned from the Ebola crisis," said Anthony Costello, WHO director for maternal, child and adolescent health.

"The reason it's a global concern is that we are worried that this could also spread back to other areas of the world where the population may not be immune," he told a news conference in Geneva on Tuesday.

"And we know that the mosquitos that carry Zika virus - if that association is confirmed - are present ... through Africa, parts of southern Europe and many parts of Asia, particularly South Asia..."

The WHO on Monday declared an international public health emergency due to Zika's link to thousands of recent birth defects in Brazil.

The WHO said last week the Zika virus was "spreading explosively" and could infect as many as 4 million people in the Americas, Standard Media reports.

He added the WHO was drafting "good guidelines" for pregnant women. The organization is also gathering experts to work on a definition of microcephaly.

Costello stressed on "Mass community engagement" in areas with the mosquitos and their breeding grounds and the development of diagnostic tools in fighting against the spread of virus.

He added that the vaccine for Zika virus might be years away.