China's Minister of Environmental Protection Zhou Shengxian on Wednesday called for the public to expose environment-damaging activities and vowed to severely punish those who commit them.

According to recent inspections carried out by the ministry, a few enterprises were found to have secretly discharged pollutants and some environmental protection authorities had loose supervision, Zhou told reporters after the opening of the annual session of the National People's Congress (NPC).

Some local governments have protected enterprises that have illegally discharged pollutants, he said.

Environment is perhaps the top concern for the Chinese public during the NPC session, which comes just days after residents in northern and eastern China were choked by heavy smog for a whole week before long-awaited showers and wind swept it away.

The prolonged smog once again highlighted the urgency of tackling environmental pollution, after decades of rapid economic growth.

On Wednesday, Chinese Premier Li Keqiang "declared war" against pollution and pledged to fight it with the same determination the country has battled poverty.

The government will take strong measures to prevent and control pollution, with the focus on mega-cities and regions with frequent smog, Li told lawmakers in his first government work report delivered at the opening of the NPC annual session.

The State Council, China's Cabinet, issued the Air Pollution Prevention and Control Action Plan in last September to deal with serious smog across the country.

The action plan requires PM2.5 (particles smaller than 2.5 microns in diameter) in populated regions and cities to be reduced significantly by 2017.