BEIJING -- The environmental authority has uncovered 140 problems during an air pollution inspection of 18 cities in north China's Beijing-Tianjin-Hebei (BTH) region and nearby areas.

Inspectors were despatched on an unannounced check of 363 government agencies and businesses, the Ministry of Environmental Protection (MEP) said Monday in an online statement.

Many local authorities need to elaborate on and improve their pollution response plans, the MEP said.

In Huairou District, Beijing, enterprises were found to be operating despite being ordered to halt or reduce production when air quality worsens. Only two companies in Suning county, Cangzhou city, North China's Hebei province, are subject to the restrictive measure.

The cities of Tianjin, Hengshui, Taiyuan and Dezhou were also criticized for "inadequate efforts."

The MEP also named and shamed enterprises that violated official policies.

Fengshi Metallurgy Material Co, in Dengfeng city, Central China's Henan province, falsified emission data to meet requirements. Zhuyou New Wall Material Co in Suning blocked the door of its boiler room, hoping to fool inspectors.

China has started to intensify the fight against air pollution as cities suffered from more smoggy days in January, with northern areas the worst affected.

The share of days with good air quality in BTH was a mere 36.2 percent last month, a year-on-year drop of 19.6 percentage points.