More than 500 alien species of plants have been introduced to China, threatening people's health and the environment, a study said.

The study, conducted by eight institutions, including Shanghai Chenshan Plant Science Research Center and Beijing Normal University, said that among the alien plants, 34 species are known to be severely harmful.

"With the rapid growth of world trade and fast development of China's economy, the alien species invasion poses risks to the country," said Chen Xiaoya, head of the Shanghai Chenshan Plant Science Research Center.

The study provides firsthand instructions for scientists and experts to take to keep the risks under control.

The study, released on Sunday, said Yunnan province tops the list with 334 alien species of plants, while the Ningxia Hui autonomous region has the fewest, with only 34.

The alien plants mainly come from South America and North America, the study said.

Based on the study, authorities plan to complete a directory on the country's alien plants in four years, and it will specify the cause, locations and harm from the species, Chen said.

Wan Fanghao, director of the department of invasive biology at the Chinese Academy of Agricultural Sciences, said invasive species can cause unexpected damage to the environment and even human health if no effective measures are taken.

"Damages from alien plants to agriculture, water environment, biosystems, forests and grassland are common these days," Wan said.

Since late October, Shanghai sanitary authorities have been engaging in a battle against the water hyacinth, with about 400,000 metric tons of the South American plant collected from the Huangpu River.

The plant, imported from Venezuela into South China in the 1950s as pig feed, blocks waterways and irrigation channels and hampers efforts to drain waterlogged fields.

Wan said with proper measures of management, prevention and control, the damage from invasive species can be minimized.

Agricultural experts have been researching chemical and biological measures to tackle the problems caused by invasive plants.

Wang Canfa, a professor at China University of Political Science and Law, said the country should establish a law against the introduction of invasive species.

wangqian@chinadaily.com.cn