Beijing, Oct 3 (IANS): An unusual spate of hornet attacks in northwest China's Shaanxi Province has killed 42 people and injured 1,640 others, the country's top health authority said Thursday.

Of the people injured in the attacks which began in July, 206 persons are receiving treatment in hospital, Xinhua reported citing the National Health and Family Planning Commission.

A guideline for diagnosing and treating hornet attack victims has been issued while local agencies have been urged to follow due procedures and ensure patients get early treatment.

The commission asked local health agencies to coordinate their hornet attack responses with agricultural, forestry and firefighting departments, including culling hornets in populous areas.

Three medical experts in critical care medicine, infectious diseases and nephrology have been sent to the field to aid in the treatment of critical patients, the commission said.

The cause of the attacks has not been officially ascertained.

Huang Rongyao, an insect control expert at the Forestry Bureau of Ankang City, the worst-hit by the hornets, attributed the trend to local vegetation growth which has increased the area populated by hornets and two months of continuous hot weather which has made the insects more active.

Hua Baozhen, a professor of entomology at Northwest Agriculture and Forestry University, however, believes the main cause is a decrease in the number of the hornets' natural enemies, including spiders and birds as a result of ecological changes.

Elsewhere, south China's Guangxi Zhuang autonomous region also reported human injuries from hornet stings between July and September.