Heavy air pollution has been reported in 139 cities in China while people celebrated the lunar new year with firecrackers and fireworks, the environment watchdog said Monday.

From 7:00 p.m. Sunday to 6:00 a.m. Monday, 92 cities were monitored as being heavy polluted in air and another 47 cities, including Beijing and Tianjin, reported severe pollution, the Ministry of Environmental Protection said.

In 338 major cities monitored by the ministry, 67 cities were clean and 271 cities were worse than the national standard.

PM2.5, a micro particulate matter that causes hazardous smog, was the major pollutant. The average PM2.5 density in the 338 cities reached 148 micrograms per cubic meter, a 27.6 percent rise year on year, it said.

Since Sunday evening, the ministry said, hourly PM2.5 density in the cities began to rise and reached a peak at sometime between 1:00 and 2:00 a.m. on Monday, when people set off firecrackers and fireworks to celebrate the lunar new year.