BEIJING - China's latest air pollution inspections have uncovered rampant violations of environmental rules among businesses, highlighting the tough battle ahead against pollution.

From early April to May 11, inspectors discovered that some 6,378 companies, or 66.7 percent of those examined, violated environmental standards, according to findings from a month of inspections across 28 cities in the Beijing-Tianjin-Hebei region and other nearby areas.

Of those, small-scale firms accounted for more than one-third as regulators struggled to properly regulate them, according to reports from the Ministry of Environmental Protection (MEP).

Excessive emissions and insufficient pollution-control equipment were among the most common problems for the inspected businesses. The MEP has asked local authorities to shut down or halt production at companies that failed to meet environmental protection standards.

The inspections are expected to last for a year.

Earlier official data showed cities in the Beijing-Tianjin-Hebei region saw more days with "good" air quality in April.

The 13 cities in the region reported good air quality on 23 days during the month on average, up 16.5 percent year on year. An average daily Air Quality Index (AQI) of less than 100 is defined as "good" under Chinese air quality standards.