Officials in Beijing had escalated the city's air pollution alert to the second highest level on Thursday as smog covers the rest of Northern China. In addition, smog had been forecasted to envelop the area for three days.

Smog alert raised to the orange level means that the concentration of particles under 2.5 microns in diameter (PM2.5) in the air posed higher risk to human health, with a tolerable amount of a maximum of 25 micrograms for a 24-hour period.

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According to the Beijing Municipal Environmental Monitoring Center (BMEMC), about 359 micrograms of PM 2.5 particulates were reported along Tiananmen Square in the Chinese capital as of 11 a.m. on Thursday.

The air quality index (AQI) had exceeded the standard 200, according to a report released by the agency at 8 in the evening on Wednesday.

AQI between 201 and 300 are considered to be "heavy" air pollution, whereas the AQI exceeding 300 may be deemed serious air pollution.

"Serious smog has appeared in the Beijing, Tianjin and Hebei region," Beijing Meteorological Bureau forecaster Li Jing stated, adding that Henan and Hebei had reported 'heavy' pollution on Wednesday.

Based on the orange alert, residents and tourists in the area are advised to minimize outdoor activities while those with weak lungs, respiratory illnesses, and the elderly are asked to stay inside their homes.

Some industrial plants are also affected by the alert as some limits are imposed to production in China's campaign against air pollution.

According to Xinhua News Agency, the smog may have been caused by farmers burning stalks in their farmlands to end the autumn harvest.

Severe traffic due to reduced visibility from the smog caused a number of roads to close in downtown Beijing while seven cities are being monitored in the province of Hebei.

Tianjin and Hebei are expected to have heavy pollution until Thursday evening.

Officials' calculations revealed that colder winds will blow away the smog on Saturday.

TagsHebei, smog