People in Beijing are choking as dense smog engulfs the Chinese capital, as well as northern and eastern China, for a fifth day on Monday, Reuters reported.

A four-tiered system divided into four categories: blue, yellow, orange and red was introduced last year as part of a plan to tackle the Chinese capital's notorious air quality problem. Smog levels hit "orange" - the second highest threat level - for the first time in the capital and a number of other cities across the country.

Orange levels mean schools are advised to cancel outdoor sports classes, while motorists are asked to restrict their vehicle use, The Metro reported.

Smog readings exceeded 200 micrograms per cubic meter on Friday - eight times the level deemed safe by the World Health Organization, Xinhua reported.

"China's pollution is at an unbearable stage," Li Junfeng, director general of the National Center for Climate Change Strategy and International Cooperation, said at a conference in Beijing Saturday according to Bloomberg News. "It's like a smoker who needs to quit smoking at once otherwise he will risk getting lung cancer."

Persistent problems with city air have prompted officials and individuals who want cleaner air to consider ways to protect their citizenry from the pollution.

Members of the Ministry of Environmental Protection cited "unfavorable meteorological conditions and firework and firecracker spree(s)" as the cause of the heavily polluted air, CNN reported.

Chinese authorities said they would shut pollution factories and limit the number of cars in an effort to remedy air quality problems that affects China, the world's biggest carbon emitter, Bloomberg News reported.

China currently uses coal for 65 percent of its energy; Li suggested the country should cut that ratio by at least two percentage points.

The country is one of the world's largest producers of green energy technology, although much of it is exported.

The smog is expected to ease towards the end of the week.