Hong Kong (CNN) The devastating armyworm pest has already spread to more than 8,500 hectares of China's grain production and could soon affect the country's entire crop, a new US government report said this week.

The voracious, inch-long fall armyworm, the larval form of the armyworm moth, can breed rapidly, spread great distances and is hugely difficult to eradicate.

In recent years the armyworm has ruined agricultural produce across Africa and the Americas, where it originated, and has now begun to march across Asia.

It has a large impact on a wide range of crops, including important Chinese staples such as rice, soybeans and corn.

According to the US report, prepared for the Department of Agriculture (USDA), it may have already spread to a range of southern Chinese provinces including Yunnan, Guangxi, Guangdong, Guizhou, Hunan and Hainan.