New research has shown a strong link between Zika infection and foetal malformations and neurological disorders, the head of the World Health Organization (WHO) has announced.

Dr Margaret Chan convened an emergency committee on the issue under the International Health Regulations, an international agreement between 196 countries to work for global health security.

Microcephaly, where babies develop an abnormally small head, is now only one of several documented birth abnormalities associated with Zika infection during pregnancy, according to the new findings.

The virus has been detected in amniotic fluid, the agency says, adding that evidence shows it can cross the placental barrier and infect the foetus.

"Substantial new clinical and epidemiological" research has strengthened the association between Zika infection and the occurrence of fetal malformations and neurological disorders. In addition, the geographical distribution of the disease is wider. The risk group is broader. And the modes of transmission now include sexual intercourse as well as mosquito bites."

The Zika virus also can affect tissues in the brain and brain stem of a developing foetus, Dr Chan concluded.

She underscored that strong public health actions should not wait for definitive scientific proof.