The World Health Organization has declared the mosquito-borne Zika virus to be a global emergency.

The disease has been linked to thousands of birth defects in Brazil and is spreading rapidly.        

The designation was recommended by a committee of independent experts to the United Nations agency, following criticism of a hesitant response so far.

The move should help fast track international action and research priorities.

The US Centers for Disease Control and Prevention said the declaration of Zika as a global health emergency will focus new attention and resources on fighting the virus.

It said the declaration "calls the world to action" on Zika.          

"CDC, along with the entire US government, is actively involved in the world's Zika response and working 24/7 to learn more about the virus and protect health."

The WHO said last week the Zika virus was "spreading explosively" and could infect as many as four million people in the Americas.          

The agency was criticised for reacting too slowly to the Ebola epidemic in West Africa which killed more than 10,000 people, and has promised to do better in future global health crises.           

The WHO's International Health Regulations emergency committee brings together experts in epidemiology, public health and infectious diseases from the Americas, Europe, Asia and Africa.

Meanwhile, Brazil's president Dilma Rousseff has said pregnant women should not travel to the Olympic Games in the country this summer because of the risks posed by the virus.