China's environmental authority found 248 companies in violation of standards during the latest round of air pollution inspection, of which over 100 were found to have discharged pollutants excessively.

Inspection teams in 28 cities in the Beijing-Tianjin-Hebei region and nearby provinces of Henan, Shandong and Shanxi have inspected 396 companies, of which 248 were found breaking the rules, the Ministry of Environmental Protection said in a statement on Thursday night.

The ministry launched the largest-ever inspection on the northern region to control air pollution, with a first group of more than 220 inspectors visiting the 28 cities since April 8. It released its findings on violations each day.

Most recently, the ministry's inspectors found a limestone factory in Beijing's Shunyi district did not have pollution control facilities and seemed to have used some machines that had already been sealed by local authorities, inspectors found.

In Tianjin, a wooden door maker was operating with neither environmental permission nor pollution controls.

The inspectors have reported the problems to local authorities for further investigation, the statement said.