Only three out of the 74 cities monitored by the government met a new air quality standard, said Wu Xiaoqing, a vice minister of environment protection.
The standard lists limits on a string of pollutants including sulphur dioxide, nitrogen dioxide and airborne particles.
It caps the average 24-hour exposure to PM 2.5 -- small particles which easily penetrate the lungs and have been linked to hundreds of thousands of premature deaths -- at 75 micrograms per cubic metre for residential areas, three times the World Health Organisation's recommended safe limit.
"The lingering smog again showed that our country's air pollution is extraordinarily severe," he told reporters on the sidelines of the annual session of the National People's Congress (NPC), China's Communist Party-led parliament.
"Emissions of those pollutants were so huge they went beyond the level the environment can bear," he said.
China's heavy and chemical industries, its reliance on coal as its main energy source, rapidly growing car emissions and widespread urban construction were the main causes, he added.