Entry-exit inspection and quarantine authorities across the nation have intercepted an increasing number of alien species and exotic pets that can pose serious risks to safety and environmental integrity, China's top authority for entry-exit inspection and quarantine said.

Authorities are remaining alert for illegal entry of such animals as spiders, tortoises and snakes, which are sent to China mostly through mailed parcels. They said they will take more measures to tighten supervision and hold law violators accountable, according to the General Administration of Customs.

Banned animals, plants and their products were found in more than 42,000 mail and parcel deliveries at ports last year, and harmful species were spotted in 5,147 of them, the administration said.

Although most banned products intercepted were meat, dairy, seeds and sprouts, illegal mailing of live animals became more rampant, spurred by the booming popularity of exotic pets in China, the administration said.

The variety of such animals intercepted at ports increased last year compared with 2016.

Most alien species were bought by individuals or pet business owners from sources in other countries, or through exchanges, the administration said.

Major alien species intercepted by quarantine authorities last year included tortoises, spiders, scorpions, snakes, frogs and various types of insects, it said. The creatures came from almost all of China's major trading partners, and were found at all major ports on the Chinese mainland, the administration said.

"In general, alien species have strong reproductive abilities, and are strongly adaptable to different environments," it said. "They may have no natural enemies in China, so they are likely to reproduce in great numbers and pose serious threats to indigenous species and will damage China's ecology, biodiversity and agricultural production if they are not properly taken care of and are set free."

Many of these animals are also carriers of diseases that could cause outbreaks among plants and animals in China, it said.

In addition, some species, such as the Brazilian killer scorpion, poison dart frogs and other poisonous frogs can be dangerous to the public and may even be used by terrorists, the administration said.

All live animals except dogs and cats are banned from being carried by passengers or sent via mail services to the mainland, unless approved by authorities and accompanied by official quarantine certificates from their country, according to Chinese regulations.

Among pets, only dogs and cats can be carried to China, and each passenger can only carry one cat or one dog each time. The dog or cat must be quarantined after arrival, according to the regulations.

Keeping track of the flow of exotic pets has been a challenge for authorities as most are light and are mailed from abroad in small amounts, the administration said.

"Tricks to evade supervision are constantly being refined, and in most cases the parcels containing the pets are disguised as other items in various forms, posing great difficulties in inspections," it said.

To make the situation worse, booming cross-border e-commerce has resulted in a rapidly increasing amount of mail and parcels each year, forcing inspection and quarantine authorities in many places to work 24 hours a day, the administration said.

Zhu Shuifang, a senior researcher at the Chinese Academy of Inspection and Quarantine, said with intensified globalization and more frequent international exchanges, cargo and mailed parcels have increased rapidly, posing great challenges in ensuring biosafety while allowing swift entry of goods.

"With so many goods, it is not possible to inspect every parcel," he said. "Advanced technologies can play a more important role in improving efficiency in inspection of harmful species to prevent loss in trade, agriculture, health and ecology."

The rapidly developing big data technology can be better applied in this regard, he said.

"For example, big data analysis can help single out passengers, cargo and mailed items that are more likely to bring in or contain banned items," Zhu said. "More government investment is needed to spur technological research and utilization in entry-exit inspection and quarantine."

The administration has taken a series of measures to improve supervision and law enforcement, including installing 37 advanced computerized tomography machines at key inspection sites for mail and express parcels, it said.

The administration will also improve cooperation with other government departments such as border control, tourism, agriculture and forestry to establish a mechanism for joint prevention and control of illegal entry of banned items to ensure biosafety and national security, it said.

Individuals who have carried or mailed banned animals, plants or their products to the mainland and tried to evade quarantine two or more times within a year will face criminal investigations by police or prosecution authorities in China, according to an amended regulation adopted in April 2017 by the Supreme People's Procuratorate and the Ministry of Public Security in an effort to check violations.

Violators face penalties of up to three years in prison and fines in serious cases, such as when violations result in widespread disease outbreaks, according to China's Criminal Law.