Wuhan, the capital of Hubei province, suffered the worst air pollution of monitored sites in the country on Thursday, with smog caused by straw burning in surrounding areas, Chutian Metropolis Daily reported on Friday.

According to data provided by the Wuhan environment protection bureau, the average concentration of PM 2.5 in the city's urban area began to rise quickly from 5 am on Thursday and reached more than 500 micrograms per cubic meter at nine monitoring points in the city's urban area in the afternoon, with the highest level of 895 micrograms/cu m recorded at the Donghu High-tech development zone.

The real-time data displayed on the official website of the Ministry of Environment Protection showed that Wuhan's air quality was the worst among the 161 monitored cities in China from 5 pm to 8 pm on Thursday.

A resident surnamed Cai said she could not see clearly when she went outside in the morning and noticed a strange odor that worsened in the afternoon.

The city government's emergency office announced on its official micro blog that the major cause of the air pollution was straw being burned in rural areas surrounding the city.

The Ministry of Environment Protection reported on Thursday afternoon that it monitored 162 sites of straw being burned in the provinces of Anhui, Hebei, Henan, Jiangsu and Shandong, and the wind direction blew the smoke to Wuhan. The monitored levels of carbon and potassium ions in the air increased eightfold, as both elements are byproducts of burning straw.

In recent years, farmers no longer use straw as fuel for cooking and heating and have no other way to dispose of it, so they burn it on their land.