China is taking steps to avert a potential outbreak of the Zika virus after the World Health Organization declared the mosquito-borne virus an international public health emergency.

The virus has been linked to thousands of birth defects in Brazil, but no travel or trade restrictions have been imposed so far.

A news release from the WHO China on Tuesday evening described the virus as "an extraordinary event" that looks set to constitute a public health risk to other countries through the international spread of disease.

This will potentially require a coordinated international response, the statement added.

Lu Hongzhou, head of the Shanghai Public Health Clinical Center, said the existence in South China of the Aedes aegypti mosquito, which harbors and spreads the Zika virus to humans through bites, and close exchanges of trade and people with South America put China at risk from imported outbreaks of the virus.

"The health authorities are drafting clinical guidelines for Zika detection and treatment," he said.

The WHO China office said the risk of Zika transmission is low during the winter in China, as the climatic conditions are not suitable for the Aedes aegypti mosquito.

But inspection and quarantine, trade, and travel agencies are on high alert.

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.