Monkeypox, a viral illness causing flu-like symptoms and skin lesions, has been spreading largely in men who have sex with men outside the countries where it is endemic.
There are vaccines and treatments available for monkeypox, although they are in limited supply.
Some global health experts said WHO may be have been hesitant to make a declaration because its January 2020 declaration that the new coronavirus represented a public health emergency was largely met with scepticism around the world.
But others said the outbreak met the criteria to be called an emergency.
Gregg Gonsalves, an associate professor of epidemiology at Yale University who advised the committee but who is not a member of WHO, said by email on Saturday that he thought the decision was "misguided".
"It met all the criteria but they decided to punt on this momentous decision," he said.
