HANGZHOU, Feb. 24 -- Travel agents across China are advising outbound tourists to be extra cautious as three of the country's five Zika patients caught the virus while on vacation.

East China's Zhejiang Province has reported three cases. All three had been on the same tour of Fiji and Samoa.

Lu Binbin, an executive with a Hangzhou travel agency, said travelers should avoid places with a Zika problem.

Symptoms of the Zika virus, which spreads to people through mosquito bites, include fever, joint pain, a rash, conjunctivitis, headache and muscle pain.

Many countries in South America have been labeled risky, including Brazil, which will host the Olympic Games this year.

Lu said the risk of infection will be reduced during the second half of the year when temperatures drop in the Southern Hemisphere.

China's National Tourism Administration has urged travelers to keep up-to-date with information from the World Health Organization, Chinese government and tourism destinations. Travel agencies also asked outbound tourists to protect themselves against mosquito bites to prevent potential infection.

With five confirmed infections, China is on high alert against the virus.

In Shanghai, health authorities have prepared emergency sickbeds and held training sessions for staff. Shanghai Public Health Clinical Center (SPHCC) plans research on how the virus develops and its long-term impact.

"Currently there is no specific treatment for the Zika virus or any vaccine to prevent infections," said Lu Hongzhou, an SPHCC professor. "We must step up efforts to stop its spread."

The National Health and Family Planning Commission urged the public to stay vigilant as the spread of the illness cannot be ruled out in some regions where the mosquito population will increase as the weather warms.

Efforts will be stepped up to quarantine the infected and reduce the number of mosquitoes, said the commission.