Beijing will shut down more than 5,500 polluting companies this year as part of ongoing efforts to improve the city's air quality.

Between January and the start of this month, the capital closed 2,086 polluting companies, affecting more than 36,000 workers, according to the Beijing Municipal Commission of Economy and Information Technology.

The enterprises were small and scattered, making it hard to track emissions, the commission said in a statement on Thursday.

Companies still using coal-fired industrial boilers have been ordered to switch to gas or clean energy boilers by Aug 1.

Last year, Beijing shut down 4,477 polluting companies, the authority added.

Small but polluting companies are also being targeted on a regional level in a yearlong environmental inspection launched by the Ministry of Environmental Protection.

The inspections, which started on April 1, have covered 28 cities in the Beijing-Tianjin-Hebei region and neighboring provinces of Shandong, Shanxi and Henan.

The latest results show inspection teams exposed 411 small polluting companies from June 10 to 13. They were concentrated in areas such as Shijiazhuang in Hebei province, Dezhou in Shandong province and Tianjin, the ministry said on Wednesday.

The ministry also highlighted repeat offenses by polluting companies. For example, Shandong Wanli Clothing Co in Heze was found to have repeatedly resumed production after inspectors ordered it to suspend production.

The ministry required all city and county governments to hand down strict punishments to small polluters to control air pollution.