China on Thursday warned of action against local officials who do not take strong steps to improve air quality in their cities, Reuters reported. “There is no jesting in war,” the environment ministry said.

Only four of 28 cities in northern China met their air quality targets in October, and PM 2.5 levels – polluting particles of width less than 2.5 micrometre – rose 5.6% on year to 38 micrograms per cubic metre in 338 Chinese cities. In contrast, the PM 2.5 levels in New Delhi and its surrounding regions consistently stayed well above 300 micrograms per cubic metre earlier in November.

The poor performance of some cities in northern China weighed on overall air quality levels in the region, Liu Youbin, spokesperson for the Ministry of Environmental Protection, said. “For those local officials who do not enforce the measures of the campaign effectively and could not improve air quality in time, we will hold them accountable,” Liu said.

China has come down heavily in recent months on its cities in its effort to check air pollution, which peaks during the winter as smog blankets northern cities because of coal-powered heating systems in homes.