Scientists have reportedly found the first evidence of a biological link between the Zika virus sweeping Latin America and microcephaly, a condition defined by unusually small heads that can result in developmental problems.

Laboratory tests found that the virus targeted key cells involved in brain development and then destroyed or disabled them, researchers at US-based Johns Hopkins' Institute for Cell Engineering said.

The findings are the first potential evidence of a link between the mosquito-borne virus and microcephaly, which until now had been circumstantial, said Guo-li Ming, a professor of neurology at Johns Hopkins' Institute and a co-leader of the research.

The researchers used lab-grown human stem cells in an experiment conducted in less than a month that they hope will aid in creating drugs to protect the cells or ease existing infections of the virus.

In a statement, the scientists said the virus "selectively infects cells that form the brain's cortex, or outer layer, making them more likely to die and less likely to divide normally and make new brain cells".

Meanwhile, the World Health Organisation's Emergency Committee will meet next week to review "evolving information" and its recommendations on travel and trade in what is thought to be high season for transmission of the mosquito-borne virus in the southern hemisphere, it said.             

Dr Bruce Aylward, WHO Executive Director for Outbreaks and Health Emergencies, said that recently published studies in the Lancet on microcephaly and by the US Centres for Disease Control (CDC) on Guillain-Barre had strengthened the case that the Zika virus is responsible.                       

"Since the public health emergency of international concern was declared (by WHO) back in February, the evidence that there may be a causal relationship has continued to accumulate," Dr Aylward said.       

French scientists, in a retrospective study of a Zika outbreak in French Polynesia in 2013-2014, said last week they had proved a link between Zika and Guillain-Barre (a nervous system disorder), suggesting countries hit by the Zika epidemic will see a rise in cases of the serious neurological condition.         

Brazil said it has confirmed more than 640 cases of microcephaly, and considers most of them to be related to Zika infections in the mothers.

Brazil is investigating more than 4,200 additional suspected cases of microcephaly.

"We're now in the high season for dengue virus transmission in the southern hemisphere, that started a month or so ago. We believe because it's the same vector, that this would be the high season obviously for Zika transmission as well," Dr Aylward said.