The World Health Organisation has declared the spread of polio is an international public health emergency.
In a statement issued in Geneva on Monday, the agency described outbreaks in Asia, Africa and the Middle East as an 'extraordinary event' and called for a co-ordinated international response.
It said the spread of the virus from Pakistan, Cameroon and Syria is the greatest threat.
Afghanistan, Equatorial Guinea, Ethiopia, Iraq, Israel, Somalia and Nigeria were also named.
The agency recommends citizens of affected countries travelling abroad carry a vaccination certificate.
Polio mainly affects children under five years old.
The BBC says the virus is transmitted through contaminated food and water, and multiplies in the intestine.
It can then invade the nervous system, causing paralysis in one in every 200 infections. It is capable of causing death.
It is only the second time in the WHO's history that the agency has made such a declaration, the first being during the swine flu pandemic of 2009.
The polio virus is endemic in Pakistan, Afghanistan, and Nigeria.