Beijing will scrutinize the feasibility of a long-term odd-even license plate system amid widespread calls for permanent clear skies, Beijing authorities said on Wednesday.

Beijing experienced two weeks of unusually clear skies during and after the Asia Pacific Economic Cooperation (APEC) summit earlier this month, which was dubbed "APEC blue" by some local residents. The smog-free days were the result of a number of measures taken by authorities, including a requirement that vehicles with odd and even-numbered license plates alternate days on the road.

With traffic congestion and smog returning to Beijing after the APEC summit, some residents have called for the government to make the temporary administrative order permanent.

"We will consider these suggestions and study whether to make the rule permanent, including extending it to the weekend," Li Shixiang, Beijing's vice mayor, said at a forum Wednesday, news portal people.com.cn reported.

"We will make unprecedented efforts to combat air pollution, so as to maintain 'APEC blue' [skies]," Li noted.

The number of motor vehicles in Beijing has surpassed 5.3 million, the China News Service reported in 2013.

Vehicle emissions contributed most of the density of PM2.5, particulate matter under 2.5 micrometers in size, in Beijing's air, accounting for 31.1 percent of local smog in the past year, Chen Tian, head of the Beijing Municipal Environment Protection Bureau, was quoted by the Beijing Youth Daily in April.