(CNN) The World Health Organization has declared the novel coronavirus outbreak a public health emergency of international concern, after an emergency committee reconvened Thursday in Geneva.

Last week, the organization said the virus did not yet constitute the emergency declaration. But with rising numbers and evidence of person-to-person transmission in a handful of cases outside of China, WHO leadership called the committee back together over concerns of a larger outbreak down the line.

"The main reason for this declaration is not because of what is happening in China, but because of what is happening in other countries," WHO Director-General Tedros Adhanom Ghebreyesus said on Thursday. "Our greatest concern is the potential for the virus to spread to countries with weaker health systems, and which are ill-prepared to deal with it."

WHO defines a public health emergency of international concern as "an extraordinary event" that constitutes a "public health risk to other States through the international spread of disease" and "to potentially require a coordinated international response." Previous emergencies have included Ebola, Zika and H1N1.

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