If heavy smog continues for more than three days Beijing will launch top level emergency efforts to reduce pollutant emissions, including restricting half of private vehicles on the road based on their license plates.

This is one of the major changes in the capital's updated emergency plan, released on Monday. The plan lowers standards for launching alerts when severe air pollution shrouds the capital, said Yao Hui, deputy head of the Beijing Municipal Environmental Protection Bureau.

Last year the capital suffered severe air pollution on 45 days but no red alert, the highest in the four-level emergency plan was issued, raising questions from the public and experts.

Under the new plan, the municipal government can issue the red alert when severe air pollution is forecast to extend for more than three days.

Based on statistics, the capital would release red alerts two or three times a year after standards are lowered, which may last for 10 days in total, said Zhang Dawei, director of the Beijing Municipal Environmental Monitoring Center.

If a red alert issued, the government will impose the toughest restrictions on pollutant emissions.

For example, use of half of private vehicles will be restricted based on odd-and-even license plates but new energy vehicles will be excluded. In addition, vehicles for government departments and institutes will have extra restrictions with 30 percent of vehicles which could be used will be banned.

Major companies in polluting industries will be suspended from production and students of primary and middle schools and kindergartens will study at home.