BEIJING - An unusual spate of hornet attacks in Northwest China's Shaanxi province has injured a total of 1,640 people, 42 of them fatally, the top health authority said on Thursday.

Among the people injured in the attacks, which began in July, 206 are receiving treatment in hospital, the National Health and Family Planning Commission said, calling for utmost efforts in treating patients and minimizing the number of casualties.

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 disease and nephrology have been sent to the field to aid the treatment of critical patients, the commission said.

The cause for 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 & Forestry University, meanwhile believes the main cause is a decrease in the number of the hornets' natural enemies, including spiders and birds, a result of ecological changes.

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