BEIJING, April 28 (Xinhua) -- China saw its air and water quality steadily improve in the first quarter of the year amid the country's constant efforts to fight pollution and sustain green development, official data showed on Sunday.

In the first quarter, the average density of PM2.5 in 339 Chinese cities at and above prefecture-level stood at 43 micrograms per cubic meter, down 6.5 percent year on year, according to the Ministry of Ecology and Environment.

The proportion of days with good air quality in these cities came in at 83.6 percent, up 3.5 percentage points compared with the same period last year, the data revealed.

The data also showed that 89.9 percent of monitored sections had fairly good surface water quality -- at or above Grade III in the country's five-tier water quality system, up 0.8 percentage points year on year. The share of surface water below Grade V, the lowest level, stood at 0.7 percent.