The spread of suffocating smog to more Chinese cities this winter came as another warning for the country to intensify its campaign against environmental damage caused by three decades of rapid growth.

In the latest attack, the smog hit 16 out of 74 monitored cities on Christmas Eve. The smog readings of the cities, which measure fine particulate that is considered dangerous, exceeded 300, or about six times the level deemed safe. A dozen cities measured “beyond index” on the pollution scale.

Official data showed that 2013 has had the smoggiest days of any year in the last 52 years. Since the beginning of December, at least 25 regions and provinces have reported high pollution levels, particularly of PM2.5, which are tiny floating particles measuring 2.5 micrometers or less in diameter. PM2.5 particles are especially hazardous as they can settle in the lungs and cause illnesses such as respiratory problems. The pollution was caused by floating pollutants from northern regions, coupled with local car emissions and adverse winter weather conditions, local authorities explained after conducting an emergency investigation. The frequency of smog-smothered days recently in southern cities like Haikou and Fuzhou, as well as western cities like Lhasa, where clean air has been a major tourist attraction, has astonished local residents. Those who can’t migrate to other places have increased their indoor time with expensive air filters installed in their apartments and have worn masks as much as possible when going out on smoggy days.

In Shanghai, the country’s eastern economic hub, the smog has affected children and elderly people who are vulnerable to the dirty air. Local hospitals treated 5,070 cases of respiratory problems between Dec. 2 and Dec. 5, marking a rise of 25.9 percent from last year.

The smog plague reflects the dual effects of China’s unchecked economic expansion, raising the pivotal issue that a new balance needs to be reached between the economy’s growth and environmental protection. The country has announced measures over the years to tackle pollution, but has made limited apparent progress. Local officials usually overlook the environmental good to go after short-term economic benefits, which will help their political careers. Meanwhile, dispersed environmental responsibilities across government departments have led to poor handling of policies.

“Smog is a bad thing, but I believe it will speed up China’s rebalancing pace, industrial restructuring and energy structure adjustment,” said Zhang Guobao, director of the Expert Advisory Committee at the National Energy Administration.

n Xinhua News Agency