Police in China have arrested around 8,500 suspects in more than 4,500 environment-related criminal cases in 2014, as the country continues to wage war against pollution, environment minister Chen Jining said Monday.

Addressing lawmakers during a bi-monthly session of the National People's Congress (NPC) Standing Committee, which will run until Wednesday, Chen said stricter enforcement of tough environmental laws were a key factor in driving down widely-feared air pollution.

Environment authorities transferred more than 2,000 cases of suspected environmental law violations to the police, more than double the figure of those over the past ten years combined.

Close to 3,400 companies and 3,700 construction sites were also found to have violated environment laws and more than 3,100 workshops were closed following air quality inspections by MEP officials and drones, the minister said.

The announcement came amid a period of heavy smog in Beijing and neighboring Tianjin municipality and Hebei Province for better part of last week.

One year after the world's second-largest economy "declared war" on pollution after decades of pursuing growth at the expense of the environment, air pollution has become one of the top concerns for Chinese citizens, particularly those living in big, industrial cities in the center and east of the country.

According to a MEP communique released earlier this month, only 16 of the 161 major cities subject to air quality monitoring met the national standards for clean air in 2014.

Chen, who was appointed environment minister in March, sounded optimistic, alleging that China's overall air quality improved in 2014 and early this year.

Average PM10 readings in 338 cities monitored by the Ministry of Environmental Protection (MEP) dropped by 2.1 percent year on year in 2014 and 5.3 percent in the first four months of this year.

Readings of PM2.5 - smaller particulate matter which can penetrate deep into the lungs, thus posing a greater health threat than PM10 - dropped11.1 percent in 2014 and 15.2 percent from January to April this year nationwide, the minister said.

Air quality changes were particularly evident in the notoriously smoggy Beijing-Tianjin-Hebei region, where PM2.5 readings recorded faster-than-average drops: 12.3 percent in 2014 and 20 percent this year, Chen said.

Chen attributed the decrease to additional government prodding and financial support, new technologies and better coordination between government ministries and among cities in the Beijing-Tianjin-Hebei region, the Pearl River Delta and the Yangtze River Delta.

Some 9.8 billion yuan was earmarked by the government for air pollution prevention and control in 2014 in addition to 2.5 billion in budget investment arrangements, Chen said, adding that government funds helped leverage private investment worth some 300 billion yuan.