BEIJING — China's air and water quality improved from late January to early June, according to the latest data from the Ministry of Ecology and Environment.

The percentage of days with good air quality was 86.9 percent in 337 cities from Jan 20 to June 6, up 4.7 percentage points year-on-year.

The average concentration of hazardous airborne particles PM2.5 was 34 micrograms per cubic meter during the period, down 15 percent year-on-year.

Data collected at 1,873 monitoring stations showed that the country's water quality also improved.

The proportion of surface water with fairly good quality — at or above Grade III in China's five-tier water quality system — rose 8.6 percentage points year-on-year, while that of surface water below Grade V, the lowest level, decreased 2.6 percentage points from a year earlier, the ministry said.