Air pollution in Beijing has reached an all time high since early this week its effect is the same as smoking 40 cigarettes a day, a study revealed.

Berkeley Earth, a U.S.-based nonprofit group has published the data they have collected by a network of sensors across China. The findings can be found in an open-access journal, PLOS ONE.

Readings of the tiny poisonous PM2.5 particles reached into the high 600s micrograms per cubic meter through the capital, as compared with the World Health Organization safe level of 25. These small particles can enter deep into the human respiratory system, and are associated with a range of harmful or even deadly diseases.

The city government has issued its first orange alert - the second highest of four warning levels - in almost two years.

"It's the worst day so far this year," said Liu Feifie, a 36-year-old mother and Internet company employee in an interview published in Yahoo. "I feel my throat totally congested with phlegm and it feels very itchy. But I'm more concerned about the health of my 7-year-old kid."

Outside Beijing, reduced visibility due to heavy fog prompted authorities to close 1,553 highway sections in central, eastern and southern China, the Transportation Ministry said on its website.

In the report by Berkeley Earth, it said that the air pollution in China kills about 4,000 people every day, about 17 percent of the total deaths in the country, but noted that connection mortality to pollution is "complicated."

Richard Muller, scientific director of Berkeley Earth and one of the paper's co-authors in a press release, "When I was last in Beijing, pollution was at the hazardous level; every hour of exposure reduced my life expectancy by 20 minutes,"

 "It's as if every man, women and child smoked 1.5 cigarettes each hour," he added.