China will "declare war" in the battle against pollution, Premier Li Keqiang said on Thursday at the closing of the National People's Congress session.

His comments explained his declaration of China's "war on smog" at the start of the annual parliamentary meeting last week, saying the government will come down with an "iron fist" against pollution.

He vowed to give harsh punishments to polluters and crack down on officials who have been negligent in solving environmental issues.