Chinese President Xi Jinping sent a congratulatory letter to the World Environment Day celebrations Wednesday, calling for joint efforts to promote green, low-carbon and sustainable development, the Xinhua News Agency reported.
World Environment Day has been held on June 5 since 1972. This year's theme is "Beat Air Pollution."
Hosting the event in Hangzhou shows China's determination to confront air pollution and share its successful experience, the United Nations said.
The event was attended by Chinese Vice Premier Han Zheng, Chinese Minister of Ecology and Environment Li Ganjie, former UN chief Ban Ki-moon, now chairman of the South Korea's National Council on Climate and Air Quality, and Joyce Msuya, Acting Executive Director of the United Nations Environment Programme (UNEP).
Since 2013, China has improved its air quality while maintaining economic growth, according to a six-year report released at the Hangzhou event.
The China Air Quality Improvement Report (2013-18), published by the Ministry of Ecology and Environment (MEE), is China's first such report.
The average concentration of PM2.5 and SO2 in the first 74 cities which have implemented the Ambient Air Quality Standard had dropped by 42 percent and 68 percent, respectively, according to the report.
Energy consumption and private vehicle ownership rose by 11 percent and 83 percent, respectively, but the concentration of air pollutants was greatly reduced, according to the report.
In the capital city of Beijing, where air pollution has been a long-time concern, the concentration of PM2.5 dropped from 89.5 to 51 micrograms per cubic meter.
Days of severe pollution or worse had fallen from 58 days a year to 15 days in a year.
All air quality improvement targets set by Chinese authorities have been met, and surveys showed rising public satisfaction, the report added.
Air quality was improved, thanks to China's rule of law, science and technology support and comprehensive emissions cuts, it concluded.
"While China has made some progress, the air pollution situation remains dire in the country," said Li Haisheng, president of the Chinese Research Academy of Environmental Sciences.
The annual average concentration of PM2.5 in over 60 percent of the cities does not meet the Ambient Air Quality standard, which is 35 micrograms per cubic meter. Cases of severe pollution remain in northern China in autumn and winter, Li noted.
The United Nations Environment Programme said nine out of 10 people in the world breathe polluted air.