China's air and water quality continued to improve in the first half of this year, as the country strengthened efforts to curb air pollution and protect water resources, the Ministry of Ecology and Environment said Tuesday.

The average density of PM2.5 -- a key indicator measuring air pollution -- came in at 29.9 micrograms per cubic meter in 339 Chinese cities at or above the prefecture level in the January-June period, which was down 6.6 percent year on year, ministry spokesperson Pei Xiaofei told a media conference.

In the first six months, 82.8 percent of days had good air quality, up 4.5 percentage points from the previous year.

The ministry also revealed that during the period, 87.4 percent of the surface-water sections and sites monitored by the country were graded Class I to III, indicating good quality, up 3 percentage points from the same period last year.

China classifies surface water quality into five grades, with Class I being the best quality. During the same period, the proportion of below-Class-V water sections declined 1.2 percentage points to 0.9 percent.