China's environmental authority on Saturday found over 2,800 companies in violation of standards during the first round of air pollution inspection.
Inspection teams in 28 cities in the Beijing-Tianjin-Hebei region and nearby areas found 2,808 of the 4,077 companies breaking the rules, Xinhua news agency cited the Environmental Protection Ministry as saying.
Problems included unlicensed production, inefficient dust prevention and lack or malfunction of pollution treatment facilities, a statement said.
Inspectors also found that some enterprises which had been closed for violations illegally resumed production and some reported fake monitoring data.
Some companies refused the inspection or prevented inspectors from carrying out their duties.
The statement said the first round of inspection ended on April 20 and the second round had already started. There will be a total of 25 rounds this year.
The share of days with good air quality in Beijing-Tianjin-Hebei rose by 14.6 percentage points from a year earlier to 66.3 per cent in March, even though the share declined in the first quarter, MEP data showed.