Women in countries hit by the Zika virus should breastfeed their babies and there is no proof the virus can spread to their infants that way, the World Health Organisation (WHO) has said.

Zika has been declared a global emergency because of its possible links to a spike in babies born with abnormally small heads in Brazil. The country has more than one million infections and the virus is spreading explosively across the Americas.

In guidance issued on Thursday, WHO said while Zika has been detected in breast milk from two mothers sickened by the virus, there are no reports of Zika being transmitted to babies via breastfeeding.

WHO said there have been no cases of babies suffering severe neurological problems or brain damage after being infected with Zika after birth.