BEIJING, Feb. 20 -- The Ministry of Environmental Protection on Thursday criticized several factories in central China's Henan Province for refusing inspections.

A porcelain factory and steel plant in Zhengzhou, Henan's provincial capital, refused to allow inspectors of environment authorities to enter their premises "using the excuse that their chief managers were not available," said a ministry statement.

Also, staff at a carbon factory stopped inspectors from filming video evidence at the site, the statement said.

The ministry inspected about 50 possible polluters in Zhengzhou and found serious problems, the statement said.

Most construction sites in Zhengzhou, especially those of utility departments, did not adopt any measures to prevent dust pollution.

Air pollution control facilities in several local factories were either out of date or under poor management, the statement said, adding that inspectors found a number of factories emitted smelly smog and thick dust.

They also found about 20 clustering small workshops producing fireproof construction material were without any pollution control facilities and were causing serious air pollution, it said.

On the same day, the ministry issued a press release on the result of an inspection operation on Xingtai City of north China's Hebei Province, neighboring Henan.

Dust control in the countryside and suburbs were not in place and several local factories, which should have been closed because of high pollution, were still under operation, the statement said.

Also, a large number of urban and rural residents in Xingtai were still using coal for heating and cooking, it added.

Hebei and Henan provinces are among those provinces suffering serious air pollution. Xingtai itself had the worst air quality in January, according to the ministry's monitoring figures.

Last month, 74 major cities under ministry monitoring only recorded 37.6 percent of days with standard air quality.