The World Health Organisation will meet later to advise on the international response to the outbreak of the Zika virus.

It comes as the number of infected people continues to rise in the Americas.

The virus is believed to be associated with serious birth defects - such as abnormally small heads - and is spread by mosquitoes.

According to the WHO, "a causal relationship between Zika virus infection and birth defects and neurological syndromes has not been established, but is strongly suspected".

The WHO will decide whether to designate the outbreak as a 'Public Health Emergency of International Concern' at its meeting in Geneva today.

The organisation says it is "supporting the scaling up and strengthening of surveillance systems in countries that have reported cases of Zika," adding that it is also prioritising the development of vaccines and new tools to control mosquito populations.

Scientists have said they could have a vaccine available for emergency use in pregnant women before the end of the year.

The Department of Foreign Affairs has issued travel advice for 20 countries in response to the outbreak.

Scientists in Brazil have said it is possible the virus is carried by the common mosquito.

Up until now, it was thought the Aedes aegypti mosquito, which is confined to the tropics, was solely spreading the virus.

Cases of the Zika virus have so far been reported in 23 countries and territories.