Farmers in East China's Zhejiang province are maintaining a 24-hour alert on the 150,000 wild boars that have been ravaging crops and injuring villagers.

Wild boars are widely found in suburban areas of Hangzhou, Quzhou, Wenzhou and Zhoushan cities in Zhejiang.

In a village in the suburb of Hangzhou's Chun'an county, this year's corn yield is expected to be reduced by one third, or 7,500 kg, due to wild boars having trampled on crops, according to local media reports.

The large number of wild boars is disrupting the food chain in these villages. Zheng Zhengshu, a villager of Chun'an county, said the number of snakes had fallen sharply as the number of wild boars proliferated, resulting in a rising number of rats that feed off the grain.

"Wild boars' ravaging crops is just a short-term affect. Once they reproduce, the food chain is very likely to be cut off, which will have a long-term impact on the whole eco-system," said Zhan Yong, an associate professor of animal science at Zhejiang University.

According to the latest survey on wild animals in Zhejiang, the number of wild boars was only 29,000 in 2000. The number jumped to 100,000 in 2006, almost tripling within six years.

This increase is not necessarily a sign of environmental improvement in Zhejiang, according to Song Zhiqiang, director of Chun'an Forestry Administration Office.

"Take Chun'an county, for example. There are more than 100,000 Chun'an residents working as migrant workers in other places. As fewer people are working in the fields on the hills, the wild boars have acquired a larger living area, so their number is growing," said Song.

In response to the situation, local farmers have resorted to using traps and electric fences to ward off the boars, though guns work best.

"Hunters are usually allowed to shoot boars during eight months of the year, but with the World Expo taking place in Shanghai, more restrictions were placed on guns," Song said.

As a result, the sanctioned period for gun use is much shorter this year and even hunters with permits from local bureau of public security have yet to be allowed to use their shotguns.

According to a local regulation on the protection of wild animals in Zhejiang, hunters are permitted to shoot 10 percent of wild boars once their number exceeds the surrounding environmental capacity.