XI'AN, Dec. 19 -- Smog has shrouded many cities from western to eastern China, including Xi'an, capital of Shaanxi Province, where air pollution reached the index limit level.

The air quality index (AQI) reading for Xi'an reached 500 on Wednesday afternoon. The reading was at the top of the AQI monitoring meter and indicated hazardous pollution, according to the national air quality monitoring website.

Smog on Thursday still blanketed the city. The AQI at noon was 417, ranking Xi'an second for having the worst pollution. The AQI in Xingtai City in north China's Hebei Province reached 491.

Xi'an City's weather forecast department said the smoggy weather, which started on Monday, is expected to continue over the next week. Air pollution levels may worsen.

The city government on Wednesday launched an emergency response because of the pollution. It suspended all construction projects and ordered at least 50 percent of government-funded vehicles off the road.

Power plants in the city have been told to limit their power generation to reduce emissions.

"I have to keep buying mouth masks for my family. Otherwise we will not go outside," said a woman surnamed Liu who was buying a mask at a pharmacy near her home in downtown Xi'an. "This is the only measure we can use to protect ourselves from the smog."

Apart from Xi'an and Xingtai, cities of Shijiazhuang and Handan in Hebei Province and Wuhan in Hubei Province also had hazardous levels of smog on Thursday, with the AQIs above 300. The AQIs in more than 11 other cities in east and central China exceeded 200, meaning heavy pollution.