World Health Organization (WHO) Director-General Margaret Chan holds a news conference after the first meeting of the International Health Regulations (IHR) Emergency Committee concerning the Zika virus and observed increase in neurological disorders and neonatal malformations in Geneva, Switzerland, February 1, 2016. [Photo/Agencies]

GENEVA/LONDON - The World Health Organization on Monday declared the mosquito-borne Zika virus to be an international public health emergency as the disease linked to thousands of birth defects in Brazil spreads rapidly.

WHO Director-General Margaret Chan told reporters an international coordinated response was needed, although restrictions on travel or trade were not necessary.

The emergency 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 WHO said last week the Zika virus was "spreading explosively" and could infect as many as 4 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.