BEIJING -- Chinese cities reported more days with good air quality in July, official data showed, as the government intensified efforts to crack down on polluters.

Last month, 338 cities monitored by the Ministry of Ecology and Environment (MEE) enjoyed good air quality on 87.7 percent of days, up by 5.1 percentage points from the same period last year.

In the Beijing-Tianjin-Hebei and surrounding regions, the share of days with good air quality during the month stood at 55 percent, a year-on-year rise of 5 percentage points, according to the ministry.

The density of PM2.5, the fine particulate matter that causes smog, in the area went down 18.4 percent to 40 micrograms per cubic meter during the month.

The city of Haikou in Hainan Province continued to have the cleanest air out of the nation's major cities, while Tangshan in Hebei Province was among the worst polluted.

After decades of rapid development that left the country with a thick, gray haze, China declared a war on pollution, with intensified efforts to crack down on polluters and incentives for clean energy use.

To clear up its air, China has been encouraging the use of natural gas instead of coal for winter heating, subsidizing new energy vehicles to curb emissions, and shutting down ineffective factories that produce the most pollution.

In the latest move, the MEE announced Thursday that it will implement a three-year action plan from this year to clamp down on environmental offenses including fabrication and interference of monitoring data.