With smog lingering over Beijing for a week, 147 industrial companies have cut or suspended production as of Tuesday as part of the city's measures to reduce pollution emissions.

City authorities on Friday initiated a response mechanism to tackle the smog. On the same day, the city upgraded the smog alert to orange, the second-highest level air pollution alert, for the first time.

Among the firms, 36 halted production, another 75 cut production in order to reduce emission discharges by 30 percent as required by the response mechanism, and another 36 firms voluntarily limited production, according to the Beijing Municipal Economic and Information Commission.

Beijing maintained its orange pollution alert on Tuesday, as the density of PM2.5, or particles smaller than 2.5 microns in diameter, measured over 400 in the city proper.