US scientists have warned the World Health Organisation the Zika virus has "explosive" pandemic potential.

Writing in a US medical journal, they encouraged the WHO to take urgent action and to heed lessons from the Ebola outbreak in 2015.

Zika, linked to shrunken brains in children, has caused panic in Brazil, where thousands of people have been infected and has now spread to some 20 countries.

Daniel R. Lucey and Lawrence O. Gostin have written in the Journal of the American Medical Association:

Mr Lucey and Mr Gostin said: "The World Health Organization Ebola Panel in July 2015 said that urgent warnings 'either did not reach senior leaders or senior leaders did not recognise their significance.'

"By many accounts the agency’s failure to act decisively cost thousands of lives."

The very process of convening the committee would catalyze international attention, funding, and research."

Referring to the Zika outbreak, they added: "An Emergency Committee should be convened urgently to advise the Director-General about the conditions necessary to declare a Public Health Emergency of International Concern."

A vaccine might be ready for testing in two years but it could be a decade before it is publicly available.