China's environmental inspectors have found that more than half of the nearly 40,000 enterprises checked have violated environmental rules.

The findings came after four months of inspections across 28 cities in the Beijing-Tianjin-Hebei region and other nearby areas, which resulted in the discovery of problems including excessive emissions and insufficient pollution control equipment, the Ministry of Environmental Protection (MEP) said Tuesday.

The inspectors, who are undertaking a year-long on-site investigation to discover the sources of air pollution in the region, exposed 7,109 companies with unauthorized locations, lacking relevant certifications, or failing to meet emission standards.

The teams also found 2,349 companies have been operating without any pollutant treatment facilities, while another 1,971 companies have pollutant treatment facilities that have been malfunctioning.

The MEP said it will require local authorities to further investigate these firms and rectify the problems.

The inspections are part of China's campaign to fight pollution and environmental degradation as decades of growth have left the country with smog, polluted water and contaminated soil.

The country started inspections amid widespread concerns about smog in its northern region.

China will soon launch a new round of central environmental inspections covering eight provincial-level areas, as the country finishes nationwide investigations into local environmental protection efforts, according to a MEP statement Monday.