North China's Tianjin Municipality issued a yellow alert for air pollution and activated emergency response measures on Saturday.
According to the city's environmental protection bureau, the Air Quality Index (AQI) reading passed 200 around noon, with the PM2.5 reading exceeding 150 micrograms per cubic meter.
Emergency measures included banning heavy trucks in the downtown area and suspending dusty construction site work.
The bureau said that increased coal consumption, unfavorable weather conditions and fireworks were to blame for the smog.
The smog will disperse Sunday, the bureau said.
Beijing, which is adjacent to Tianjin, issued a blue alert for air pollution on Friday.
Hangzhou, a city in east China's Zhejiang Province, which banned fireworks displays in its six main districts, reported improved air quality over the Spring Festival week.
On midnight Jan. 28, the Lunar New Year's Eve, the traditional time to set off fireworks, the PM2.5 density was 42 micrograms per cubic meter, the lowest in five years.
