Municipal workers gesture before spraying insecticide at the neighborhood of Imbiribeira in Recife, Brazil, January 26, 2016. The operation is part of the city's effort to prevent the spread of Zika's vector, the Aedes aegypti mosquito, according to a statement from Municipal Health Secretary. [Photo/Agencies]

A notice issued by the General Administration of Quality Supervision, Inspection and Quarantine said travelers arriving from Zika-hit areas must report suspected symptoms. Quarantine checks have also been stepped up for cargo arriving from these areas.

Bernhard Schwartlander, the WHO representative in China, said, "The WHO is working closely with the Chinese health authorities to discuss the implications of this public health emergency of international concern."

But he said the risk of a widespread outbreak of the Zika virus in China currently appears to be low.

In general, the symptoms known to be caused by the virus tend to be mild. They include fever, a rash, pain in the joints and conjunctivitis.

Symptoms usually occur two to seven days after infection. Many people who are infected do not show any symptoms, and those who do can be treated easily.