The World Health Organization will hold an emergency committee on Monday to decide if the Zika virus outbreak should be declared an international health emergency.
At a special meeting in Geneva, WHO Director-General Dr. Margaret Chan said the virus - which has been linked to birth defects and neurological problems - was "spreading explosively."
Zika virus was first detected in 1947 and for decades, only caused mild symptoms.
But Dr Chan said "the situation today is dramatically different".
According to the US Centers for Disease Control, the Zika virus is now in more than 20 countries, mostly in Central and South America, with predictions between three and four million could be infected this year.
A Sydney virologist has confirmed Australian travellers have returned from South America carrying the virus, which is mosquito-borne.
The Department of Foreign Affairs and Trade's Smartraveller website has added advice on Zika to a number countries in response to the "rapidly evolving situation".
Professor Dominic Dwyer told the ABC experts did not know whether Australian mosquitoes could pass the virus onto others here.
"There have been some people who have come back to Australia who've had Zika virus infection," he told the ABC.
"The main mosquito carriers of the virus are not present to any great degree in Australia, except perhaps up in the top end of Queensland.
"But we're not entirely sure yet whether some of the Australian mosquitoes could carry Zika virus."
DFAT is urging pregnant women to reconsider visiting 22 nations in the Caribbean, Central America, South America, Africa and the Pacific Islands where Zika is transmitted.
Previously, only five country advisories contained information about Zika.
Dr Chan said although there was no definitive proof that the Zika virus was responsible for a spike in the number of babies being born with abnormally small heads in Brazil, "the level of alarm is extremely high."
She also noted a possible relationship between Zika infection and Guillain-Barre syndrome, which can cause temporary paralysis.
"The possible links, only recently suspected, have rapidly changed the risk profile of Zika from a mild threat to one of alarming proportions," Chan said.
There is no specific treatment or vaccine for Zika, which is related to dengue - scientists have struggled for years to develop a dengue vaccine but have failed to create a viable shot so far.
The UN health agency last declared an international emergency over the devastating 2014 Ebola outbreak in West Africa, which ended up killing more than 11,000 people.
© Nine Digital Pty Ltd 2017