China's top health authority has issued a public alert for dengue fever and malaria, which pose a risk to more than half the world's population.

The alert was announced at a news conference on Thursday by the National Health and Family Planning Commission to mark World Health Day, which is celebrated on Monday, the anniversary of the founding of the World Health Organization in 1948.

The commission's focus this year is on pathogens and parasites that spread via certain "vectors", or paths - via mosquitoes, sandflies and ticks - or from one infected animal to another, including humans. Besides dengue fever and malaria, bubonic plague and epidemic encephalitis B are concerns.

"Dengue, in particular, poses serious health challenges for the public, and increasing regional and global transmittal in recent years has made intervention efforts even harder," said Zhang Yong, deputy director of the commission's disease prevention and control bureau.

Last month, eight imported dengue cases were detected among a group of 28 Chinese returning to Chongqing from a trip to Indonesia and Singapore, according to the General Administration of Quality Supervision, Inspection and Quarantine.

Worldwide, dengue is the fastest growing vector-borne disease, having recorded a 30-fold increase in the number of cases in 50 years, according to the WHO.

More than 40 percent of the world's population is now at risk from dengue and there are about 100 million cases each year worldwide, the WHO estimates.

In China, dengue has been mainly detected in the southeast costal and southwest areas, according to Liu Qiyong, a senior specialist at the Chinese Center for Disease Control and Prevention.

The center has begun monitoring major vector-borne diseases in 19 provinces.

In general, they have been declining, said Liu, citing constant efforts to curb epidemics.

However, emerging challenges in recent years have made the fight against them more complicated, he said - factors such as globalization, climate change and the gap between quick urbanization and a limited supply of public health services.

The annual number of imported diseases, particularly dengue and malaria, that are intercepted by the authorities has been rising, official statistics show.

Notably, imported malaria cases accounted for more than 90 percent of the reported total in 2013.

In addition, global warming has expanded the traditional habitat of the types of mosquitoes that carry and spread infections, putting more people at risk of contracting dengue fever, he said.

Worse, blank areas remain in the center's current monitoring efforts, so it can be hard to assess risks, provide alerts and make timely and accurately intervention plans, he said.

Moreover, public awareness needs to be improved, he said.

Individuals traveling to infected areas or countries should take precautions against infection to avoid bringing the infections home, he said.

At State level, effective intervention requires cross-border cooperation, he said.

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