BEIJING, May 5 -- The Chinese government has warned farmers of an impending crackdown if they violate a ban on burning crop stubble in an effort to improve air quality in and around Olympic host cities.

The ban runs from May to the end of September in Beijing, Tianjin, Hebei, Henan, Shandong, Shanxi, Anhui, Jiangsu and Liaoning, all areas around Olympic venues, said a directive from the ministries of environment protection and agriculture.

Beijing has been plagued by air pollution caused by crop stubble burning in areas around the capital over the years. In June last year, two days with very bad air quality were blamed on such activities.

The Ministry of Environment Protection also monitored aggravating crop stalk burning in major agricultural provinces like Hebei, Henan, Shandong, Jiangsu and Anhui from May to June last year to compare with the same period the previous year, the report said.

Farmers in China often burn crop stalks left after the harvest to clear the fields for the next planting.

The two ministries directed their respective local bureaus in the nine provinces and municipalities to step up surveillance and prosecution of stalk burning.

From May to September, the Environment Protection Ministry would use satellites to monitor the burning of crop stalks across the country and publish the results in the media, the Beijing News reported on Monday.

Beijing and six other cities are to co-host events for the Olympics, which begin on August 8.