The increased alert came with an health advisory for children and the elderly, and a request for citizens to use public transportation, China's state-run Xinhua News Agency reported.
Orange is the second-highest level on the city's alert system.
The air pollution in Beijing is currently 15 times above the daily maximum recommended by the World Health Organization, the BBC reported.
Notable deaths of 2014 [PHOTOS]
U.N. investigator: prosecute North Korea