BEIJING, June 12 (Xinhua) -- China's air and water quality improved over the past five months, said a report issued by China's Ministry of Ecology and Environment Friday.

The report showed that 80.7 percent of surface water quality was graded Class I to III (good water quality) in the first five months, up 6 percentage points from the same period last year, while that of Class V fell by 3.5 percentage points year on year to 1.4 percent.

Surface water quality in China is divided into five classes, with Class I being the best.

For major rivers, including the Yangtze River and the Yellow River, 84.4 percent of the water quality was graded Class I to III, up 6.6 percentage points year on year, and 1.1 percent was graded as Class V, down 4.1 percentage points year on year.

The percentage of days with good air quality was 84.9 percent in 337 cities at and above the prefecture-level from January to May, up 4.6 percentage points year on year. The average concentration of PM2.5 (atmospheric particulate matter) was 39 micrograms per cubic meter in the January-May period, down 11.4 percent year on year.

Among the cities, Haikou in Hainan Province, Lhasa in Tibet Autonomous Region and Zhuhai in Guangdong Province ranked as the top three for good air quality in the first five months.