Beijing - Quarantine authorities are warning millions of holiday revelers not to bring hazardous plants and animals into the country when they return from trips abroad during the weeklong National Day holiday.

More than 530 million people are expected to travel during the traditional fall break, an increase of nearly 10 percent from the same period last year, according to an official prediction.

And recent disease outbreaks are making them more and more likely to pose a hazard to public health when they return. The World Health Organization - the health authority within the United Nations - and the General Administration of Quality Supervision, Inspection and Quarantine have reported outbreaks of Dengue Fever in southeast Asian countries, West Nile fever in parts of Europe and cholera in African countries.

Travelers, to prevent their trip and shopping plans from being affected, should learn about health regulations and abide by them, the Shanghai Entry-Exit Inspection and Quarantine Bureau said.

The quarantine authority in the Guangxi Zhuang autonomous region, which borders Vietnam, also said it will conduct stricter inspections in order to prevent diseases from spreading to China, Xinhua News Agency reported.

Border authorities will confiscate any contraband travelers try to import. Meanwhile, travelers are being asked to obtain authorities' permission before bringing blood, human organs, foods, plants and similar things in to the country, the Guangxi Enter-Exit Inspection and Quarantine said.

It said 3,040 contraband shipments of plants and animals were found among travelers' belongings or parcel posts from January to September this year.

Wang Zhanjun, a senior official with the Guangxi inspection and quarantine authority, told Xinhua that certain handicrafts, such as those made of rosewood, should not be imported because they often carry the eggs of the mosquitoes and flies that spread Dengue Fever.

Li Xinjian, a professor at Beijing International Studies University's school of tourism management, said the large number of people who can be expected to travel during the holiday week will make it difficult to prevent contraband from entering the country.

"Many of them are not aware of the consequences and would like to bring local foods, fruits and products in and out to share with their friends," Li said.

Many large cities are seeing more and more people come and go from China.

On Sept 30 alone, more than 98,400 people flew in and out of Shenzhen.

Border control authorities estimate 656,000 international travelers will enter and exit the city from Oct 1 to Oct 7, 32.3 percent more than this past year.

Two Shanghai airports, meanwhile, had accommodated 54,000 international passengers by 4 pm on the first day of the holiday. Of those, 42 percent were Chinese.