Environmental watchdogs strengthened inspections to reduce pollutant emissions as the air quality deteriorated on Monday to the most severe readings in the country's northern regions, including the worst this year in Beijing.

Beijing required over 2,100 major companies in polluting industries to suspend their production. It also ordered all construction sites to stop work as well to cut emissions, after issuing an orange alert, the second-highest response to air pollution, on Sunday.

The Ministry of Environmental Protection has sent several inspection teams to supervise the implementation, saying on Monday that at least 11 construction sites and cement-making plants continued to work despite the restriction.